I think it's always good to network and to keep your interviewing skills sharpened. You never know which employer you talk to might be good for you, and which ones might have referrals for you.
The best approach is to go in and find out what they need, without saying anything that implies you would never consider working on site. Right now, all of your business comes from one client - and that's great if you are happy and they are as well. My husband is a self-employed copywriter, and he has seen great clients and also terrible ones. If anything should happen with your client (buy-out, gets sold, goes bankrupt, new owner/managers who have a nephew in the bookkeeping field, they get a "pitch" from someone else doing the same service), you could be out of a job with zero income and zero notice/severance.
Some clients are leery of off-site work because they really have a hands-on approach to management. My husband had one client who absolutely had an old-school approach, and thought the only way a good writer could work was to sit in a cubicle with a lousy computer and a bunch of noisy co-workers, spending half his time in brainstorming meetings so the boss could shoot down any idea before it was fleshed out. The idea of providing good input and then letter the writer work in quiet without interruptions (providing a first draft that is 90% on strategy every time was completely foreign. Some employers think that off-site employees won't be focused and will gouge them for hourly rates when they weren't working. They worry about people being accountable and being self-starters. Sometimes they worry about confidentiality, but truly, in the computer age, nothing is safe whether you're working at home or on site.
On the other hand, there are many companies who see advantages to having someone off site - reduced office expenses, no desk/computer/office supplies, no workers comp insurance, no health benefits, no paid vacation time, and so on. They know how to look at the job and see that it's getting done, with less focus on whether you did it at 9 AM or 10 PM and less focus on whether it actually took you the estimated 6 hours or whether you got it done in 4. They know what the job is worth, and they don't care how you got it done.
You only have Tammy's info on what they are looking for - so you don't know for sure that this is accurate. Maybe they are flexible, maybe they aren't. Tammy may be interested in a referral bonus too - but maybe she would get that no matter where you worked. And maybe they'd feel better about hiring a friend of an employee if that friend worked off site. So you have to gather some info.
You can't contact a company to solicit business that's different from what they are offering. But you can try to get an interview and then size things up. The approach you might take is that you are interested in expanding your opportunities, you're a hard worker, and you've heard they are a great company. They may have other opportunities that you and Tammy don't know about, they may have something in 2 months and come back to you, they might love the idea of someone working off site and not costing them as much. You've done a lot of work for one client exclusively, so that might appeal to them. You don't have to tell them right now that you'd will or won't do something. You start out showing them you are open, you are looking for a "good fit" whatever that entails. Don't tip your hand about the hours you are willing to work.
Most employers understand that a lot of women work part time when their kids are little, so you don't have to explain much about that. You don't have to answer questions about your home life and how you will get Susie to dance class if you have a job. You don't have to say you are looking to leave the house or not leave the house. You simply say that you have been a terrific bookkeeper and your client has kept you on for so many years because of that. This proves you are loyal, reliable, accurate, honest and discreet - all things they need in an accountant. You say something vague like "this is a good time to explore new opportunities." You say you have great time management skills, that working at home gave you and your client distinct advantages. You are a self-starter and very organized, the client has liked having someone they didn't have certain costs for and they found it a real savings. Then you stop talking about that and just let it sit with them.
You ask about the job, you let them tell you what they are looking for. Look interested, ask good questions. Don't ask them yet whether they would consider an off-site person. Just learn as much as you can. Is this a company you would even consider working for off-site? If you hate them and think they are shady or domineering, it's not even an issue. When you discuss your own job, make sure you are highlighting the skills you use, how you interact/interface with your supervisor at the company, how you have grown, what new challenges you have faced and how you solved their problems/saved them money. Show how you have helped their bottom line.
If they ask "Why are you looking for full time work?" then you say you continue to build your business and develop your skill set, and you are looking for new challenges. Make it clear, without actually saying so, that you are looking for WORK and not looking for medical insurance, paid vacation, and so on. Don't ask about salary - you never ask about that on the first interview anyway, even if you do want to work on site. If they bring it up, that's something else again.
Be prepared that they may ask you how you will tell your current client that you won't be working for them anymore. Duck that question by saying something about almost all employment is at-will, and just as employees give notice and employers make new hires, freelance employment relationships can and do go through changes. While you are happy with them and they are happy with you, in the current economic climate, it's never wise for either of you to put all your eggs in one basket.
If they want you, they will ask for another interview or maybe even go straight to making you an offer. At that point, you can say you don't think it's a good fit at this time, or that you have such a great situation that you don't think it's the right time for you to be on site 40 hours a week. Don't say your kids need you - make it more about the work schedule and flexibility. Reiterate that you like Tammy's company very much (if you do) and you would love to do some contract work for them if the opportunity arises. Don't let anything imply that you wasted their time and never had any intention of working there. You always want them to be so glad they met you so they will speak highly of you, and so they will think of you first if they have something that needs to be farmed out. For all you know, next week their president could tell the HR people that he wants to lower his insurance rates and he wants to hire some freelancers. Or maybe the boss knows someone else in another accounting firm who DOES need someone like you. I got a call once from a person I'd never heard of - but I had interviewed somewhere else, it wasn't the right job, but I impressed the interviewer enough that, when another colleague called her for leads, she said, "Well, maybe you should talk to this D. person I interviewed - she wasn't right for our job but she's dynamic and smart"…blah blah. Next thing you know, I had an interview and a job offer.
Maybe they would have something for a person who comes in for a couple of hours a week, or at the start of a project. That's what my husband does sometimes - he goes in for an "input meeting" to meet some people and maybe with a new client, because it looks good for the agency if they put their creative team in the room together. Then he goes to our home office and does all the work, and the client is happy because they agency is getting it done, regardless of which office the creative person is sitting in. Half the time the client doesn't even know that my husband is a freelancer.
Anyway, I think interview and client contact experience is always a good thing. Maybe in a year you'd want to have a full time job, and it's always good if you've left a good impression.
And don't share any of this info with Tammy - the conversations must be between you and their HR people or whoever is interviewing. DO NOT tell Tammy you aren't considering full time work. Just say "I'd love to talk to them and see if this is a good fit. Thanks for the referral."
