50 watts seems quite light for drums, especially kick drum. Of course, it depends on how much volume is needed and what the budget it. I like Peter's idea, but if that's too much stuff and simple and cheap is needed, a Peavey KB 300 can be had quite cheap. It's heavy, but that's the trade off.
Also, most powered speakers have a line in, so she could use any number of them (QSC makes some really nice ones).