Recumbent or upright. Tadpole (2 wheels in front) or delta (2 wheels in rear)? If recumbent, you may want to post on
Bent Rider Online. Trike dealers are scarce in most areas, unfortunately. There are some online vendors though. If she has developed this interest from a friend or acquaintance, perhaps that person would have some good leads.
I did a search of Terra Trike vendors and there is one in the KC area: Bike America. There website shows a few trikes, but that does not mean that they stock them.
Good luck.