medications have a purpose. They make the person feel better and more in control so they can work on the issues. It is not a lifetime decision.
If I were your doc and you told me that you did not want to do the meds I would tell you to let us know when you were ready to start them and to make the first therapy session for a few weeks after she starts.
The medication will make therapy move faster and allow it to be much less stressful and make is more productive.
I think that medications are not a fix all but are a tool to make things easier to deal with when you are pulling them out and looking at them straight up.
You child is going to have a harder time and will end up taking much longer to work through her issues without meds.
Think of it like surgery. If you are going to have your appendix out do you want to do it without meds? Of course not. You want to have it out the easiest way possible. Same with working through stressful issues. Pulling the wound open and pulling the stressors out to look at them and trying to find new coping skills or ways to deal with them is hard, meds just make life more stable and less likely to spiral out of control.
People in therapy often need to take a short term med to help them stay relaxed and not react in the opposite direction to where they are wanting the therapy to go.
If you still choose to not medicate her then please be aware that you will likely see a drastic increase in her controlling ways and even more depression and anxiety the whole time she is in therapy.
When your life feels out of control you try to over control areas of your life that you get the least opposition in. For example, she bosses her little brother around. She knows he can't hurt her or cause her mental pain. So she tries to control him so she can find some control in any way she can.
I used to sing with a group. Hubby and I were having a lot of issues and I was super stressed out at home. So when I went to practice I often would tell other people how to sing their parts, how to pay their instrument, how to dress, I would try and control every little thing around me in this group. They noticed but realized what I was doing. They let me know I needed to stop but that they loved me anyway.
I found somewhere I could feel like I was in control so that I could build that safe feeling. When I took some anxiety meds for a couple of years the lack of control in those stressful areas didn't bother me as much so I become less controlling in areas I could be bossy.
Same with your daughter. She is going to be way more controlling and stressed out while doing therapy without at least a small amount of anxiety meds to help her stay stable.