Welcome here to the Forum. I'm sorry you have such a difficult and worry situation to face. Knowing what's best for one's child is often not straightforward.
A couple of things do stand out, the first is that if I understand correctly you post is saying her existing medication is responsible for making her anxious. The second is that at least in part you are concerned about the long term effects of further medication to combat this.
So I guess the first thing to ask is can the current medication type - or dosage - be varied to prevent anxiety? My apologies if you have already looked into this. It my be a second opinion might be helpful here. This is not going behind anyone's back, just information gathering on a serious subject.
I've no knowledge about medications for ADHD, and have ben on meds for PTSD, anxiety and occasional bouts of depression for a very long time. One the correct regime was found I've been able to live a reasonable life as a result and do not contemplate going off them. Than again I did not start on them until an adult.
I guess in the final analysis you may have to be guided by professional opinion, however you do not necessarily had to accept the first one you receive without further inquiries