if your sister is taking medications, particularly if she takes valproate (Depakote or Depakene) which is a common epilepsy drug, it is important to see a dr to discuss the pros and cons of staying on the medication.

valproate can cause cardiovascular or neural tube issues in the unborn baby, meural tube issues occur in about 1% of pregnancies where mums are on valproate. these often won't be detected until 2nd tri.

maybe the gp has checked her meds and they are ok to stay on during pregnancy, and the specialist appt is just to double check.
As far as i am aware she is on Tegretol which i believe is not safe for most women to take whilst pregnant. I'm just concerned that the doctor she saw isn't taking her condition seriously. She's told me that the specialist appt is to change the meds.