I could be a TIA but there are other possibilities that I can think of but more information is required to assess whether this is the case.
You say that your cousin is on epilepsy medication. May I ask whether she has epilepsy or whether she is on that medication for another reason?
May I also ask how long she has been on this medication?
Besides a TIA two other possible reasons spring to mind:
a) she may be experiencing a side effect from the medication, either an early reaction if the medication has been recently prescribed or because she has been on the same medication for a prolonged period. It can be a side effect of some epilepsy medications.
b) if she does have epilepsy it is possible that she has developed aphasia. This is not uncommon, although the % of people with epilepsy who are affected is not high.
It does worry me when you say that she left you a jumbled up message. You do not say if it was a spoken or written message. If it was a written message it is less likely that she was experiencing a period of aphasia since it can be "worked around" in writing. If it was in writing it is much more indicative of a TIA.
I do suggest that medical advice be sought as soon as possible.