If she learned HTML on her own volition, then yeah I think you should go with javascript to add interactivity to her creations. If you get the feeling she's interested in the computational aspect of it, definitely show her python.

Another approach would be to code up a simple interactive python script and let her run it. It could be a number guessing game (she tries to guess a randomly generated number, it tells you if your guess is low or high and she has a certain number of tries). Or it could be a mad lib game (she enters a noun, verb, adjective, etc. and it spits back a funny story/sentence). It depends on the kind of kid she is. You could help her code up a version of her own and go from there.