I'm sorry, but I don't think that most photographers understand what it means to backpack with gear. A tripod? for a beginner? an external flash?
her XT already has a flash. I have backpacked for the past 10 months in Asia, and it's a pain in the as$ carrying extra stuff around, and strapping a giant tripod on my bag or carrying an external flash for a beginner is like telling my mom to put nitrous in her prius.
way overkill. I understand that lighting is essential, and tripods help a ton, but please.... for a beginner, or someone not that interested at the moment, more accessories to make life more confusing, and her bag heavier is a bad idea.
i agree that the 50mm would be good, but on a crop, its too tight.
i'd upgrade to the 18-55 IS II if possible, and call it a day. or get an S100 or something like that. otherwise, just tell her to enjoy what she has and use it
Backpack? Where in the OP's question does the word "backpack" appear? It is nice that you have been to the hemisphere referenced in the OP, but not all elements of your experience apply to this trip to India.
I do not think a speedlite is terribly more complicated (or large, or heavy) than the built-in flash, but it does allow for bounce light indoors, and more power. I am not sure how excited one can or should become at the prospect of replacing an 18-55 I with an 18-55 II as you suggest, or if that would even be worth the price. And getting this person interested in photography was one of the OP's stated aspirations.
I only listed "tripod" and "50 1.8" because you could buy either one with the money left over on @$200.00 after buying the flash. Even if she does not need a tripod on the trip, upon her return a tripod is a very basic cheap thing for a photographer to have. The 50mm would be GREAT on the trip; feather light, teeny-tiny portable, and fantastic in low light compared to the kit zoom.