Hi and welcome to the Chiari forum.
May I ask how old your daughter is, and why it was just DX 3 years ago? If she has type two, this should have been seen at birth.
Pregabalin is a generic of Lyrica and the possible side effects are similar to what she is dealing with as symptoms of Chiari so, I personally do not see how it could be effective.
Does she have a true Chiari specialist, and has she had other related conditions ruled out?