Posterior Fossa surgery has little to do in the long run with travel.
A/C Cabins are pressurized to about 6000 ft.
Ask a real doctor - an ENT or Neuro surgeon, not some clueless family practice person.
M (MD ABIM,ABNM,ABR)

One of the House Ear Institute's specialties is treating disorders related to facial nerve, acoustic tumors and the balance system.

Since they understand her condition well, they would be best able to advise her re: any equilibrium issues or pressurization fears she might have. Btw, you might be interested to know that the House Ear Institute developed special ear plugs called Ear-Planes that are supposed to help with ear pain while flying. My mom uses them and says they help her quite a bit.