I would say before, let it dry then draw. But that is entirely a guess. Thing is you don't want her to spend ages drawing the map then the tea ruins it! Could you use a brown crayon and lightly colour the paper instead?
Thats what i though kbear but i wondered whether the effect would then be spoiled when she drew on the paper. I don't think she'll want to do the crayon thing - she's really keen on using the teabag for soem reason.