It is perfectly normal to have anxiety about leaving your child with someone that is not you or your mate. I am not sure if you ever reconcile these feelings, but the key is finding the "right" person. We went through 3 babysitters before I found someone that I am completely confrontable with. One was even my FIL. He loved the kids, but he didn't give them enough structure. He let them do whatever they wanted because he was grandpa and didn't want them to be mad at him. I understand his point of view, but I also need to know that the individual who is watching my children is going to listen to what I say versus what a 4 and 2 year old tell them. We tried a daycare facility and did not have a good experience. We also tried a woman that I found on Craig's List. She also loved the kids to death, but would feed them ice cream for breakfast and loose their shoes/shorts/diaper wipes/etc. Then I found a woman who was advertising in the paper. I never thought I would allow a stranger to be responsible for my children, but it has worked out wonderfully. We visited her home 3 times prior to leaving the kids there. We eased into the transition by doing a view hours/days at a time and later even did surprise early pickup times. We have never found anything that concerned us.
I do have to clarify that as a parent I am not always thrilled about some of the happens at the babysitters. After all this woman is not me and therefore cannot handle everything in exactly the same manner as I would. That was the hardest thing to reconcile with myself. However, she is great with the kids. She follows every instruction I give her and she keeps the kids safe. That is what I am paying her to do. I am not paying her to be their parent. She just can't be. That role is already taken.
Of course you are going to think about your child when you go back to work, you have been with her every day for two years. I have been back to work for 3 years now and occassionally I think about my kids, but it is more jealousy that I am not home than worrying about their safety. They key is finding the right person even if it isn't family and the anxiety will wear off.
I also needed the adult interaction. I stayed home with my son for six months and really started feeling isolated from the outside world. Then when I had my daughter, I stayed home for 3 months. I do have to mention that I am fortunate that I only work 3 days a week. It is enough that I get to mingle with the outside world and still get to spend time with my children.