Another vote from me to NOT get a cheap guitar. Like Slipin Lizard mentioned, if it's bad then it has a bigger chance of turning someone away from guitar. If the frets don't sound right, or you can't tune it, it'll be a complete waste of time and money. I'd go to Guitar Center and ask them. You can tell them you want something inexpensive, but not too cheap in quality. I'd go to maybe a couple GC's if you can though, or at least talk to a couple people and get opinions. Just to make sure they aren't trying to rip you off or selling you something more expensive than you need.

Buying used is also a good tip, but then you have to rely more on your own knowledge of the guitar to determine if it is a good but.

Think of it as an investment. Sure you may have to pay a little and it may end up just being money lost if she doesn't like it, but imagine where it could go if she DID like it. You won't regret spending the money then.