Well, my big question is how much money are you willing to spend?

This isn't a cheap hobby, and there are a lot of different options that are pretty much capped by what you want to spend into it.

Personally, I would NOT recommend Ableton to someone just getting into this. Something along the lines of Virtual DJ or Traktor would probably work better. And honestly, if you can afford it, the VCI-300 with ITCH really is a GREAT beginner controller. But it's not cheap.

What's your price point? What kind of music will she be mixing? Do you just want software, or are you looking for hardware as well?

There's a lot of questions left unanswered before I'd jump on any of these above "conclusions".