First of all what are the medications prescribed for? Asperger's Syndrome is a developmental disability and medications can't really do much except stop aggressive behavior from what I know. But people with Asperger's can have a psychiatric disability as well and medication does treat that (if you are posting in the bipolar forum, perhaps that's what the medications are for?). Generally going off medications is not a good idea and if it is done must be with a psychiatrist's specific titration schedule. Depakoate is a mood stabilizer that can cause weight gain. Lamictal as an example is less likely. As regards antipsychotics, Abilify is the least likely to cause weight gain. Why not ask her psychiatrist about available options? We have some good websites linked up such as "Depression Central" that you could read for informational purposes and then discuss with her psychiatrist.
Depakote has to be reduced very slowly. As it is an anti-seziure med a sudden drop in dose could cause a seizure. It is very dangerous to just stop.
Your psych will discuss a weaning off programme with you and no doubt start to introduce a replacement mood stabilizer before the depakote is completely out of the system.
Having had to come off depakote myself I can tell you that I had some terrible migraines and "spaced out" feelings. It was not a nice experience. The weight I had gained (although not huge) did take about 3 months to come off.
Agree with bulldozer re "weaning off" and would like to add that seroquel has significant weight gain side effects as well.
This weight medication / wellness / weight gain is a tough dilemma, it's a real balancing act and you should express any concerns to your doctor.
Ceasing medications without a doctor is a no-no - I'm sure you understand this.
Finally, I'd say yes, going off the meds will probably stop the weight gain, both of the medications you mention can have this effect.