It is more than likely that this is not situational depression caused by a specific event or events. Depression is often caused by chemical imbalances and can't be "shaken off" no matter what. Robin Williams is a perfect example. Depression is an illness that medication can help.
I don't think the doctor will tell you about what they talk about, but I'm almost positive that you will be included in decisions about meds. Most important, keep an open line of communication with your daughter. Don't be judgmental and as hard as it is, be patient with her and the depression. Depression can be a lifelong disease.
It's great that your daughter opened up to you and that you listened. If they do suggest meds, be very active in the process. It can take awhile to get dosages right and sometimes the side effects are not fun. But stick with it. If her depression is caused by a chemical imbalance, it won't just go away.
You and your husband might also benefit from some counseling. Not because you are having problems, but because it can help you help your daughter.
Let her know that no matter what, you are there for her. If she needs someone to listen, if she needs to cry for no apparent reason, if she needs a hug. But at the same time be sure you aren't suffocating her. Speaking from experience, that can be almost as bad as feeling alone.
And although this sounds scary, be aware of the signs of suicide. And don't be afraid to talk about it with your daughter. I saw a great video that Mayo Clinic did about talking about suicide.
https://m.youtube.com/watch?v=3BByqa7bhto
Take care!