M.P.
What's the worst that can happen? She talks too much. It's the first day. The teacher isn't going to be concerned. Dealing with issues that medication helps is a matter of trial and error. Does she have ADD/ADHD? If so, that's common and the teacher will be understanding.
There are many different meds for this and you can try a different one if she still needs meds.
I suspect that you've had so much emotional turmoil because you're overly conscientious and have negative thoughts about needing help. That's what the "safe seat" and talking with the counselor are. They are ways to help a child who has difficulties. Having to use them is not a bad thing. It's good that they're available.
My daughter, who is now 30, and now my granddaughter were in a special group that met weekly with the school counselor. It was called a friendship group but was like group therapy for kids who have difficulty knowing when certain behavior is appropriate or not. The groups were definitely a positive thing.
My granddaughter also takes medication for ADHD and had an IEP. She received extra help in reading and math. Again good that the school can provide extra help for kids with difficulties.
Your daughter is a wonderful addition to the world and as time goes on will be able to function appropriately and successfully because she has received extra help. Look at these experiences as a way to help her learn. You are a good parent and she is a good child. Needing help does not detract from that.
You've gone thru alot to get her to this stage. She is not going to regress from 5th grade back to kindergarten. She's learned much and tho she may have difficulty with talking too much, not paying good enough attention, etc. The teacher and the counselor are there to help you both find a way to help her have success.
So relax, knowing that what will be will be and that there are people there to help you.