Well, what exactly does "PTSD type medication" mean? Some sort of SSRI? It is generally best to avoid taking any medication concurrently with ayahuasca, but DMT alone is a different story.
Personally, I would also recommend that she not go into the experience expecting it to cure her depression. Psychedelics may have some potential to aid in the treatment of certain mental health problems, but it's highly unlikely that one single experience is going to magically cure her for life.