A lot of beginners find something steeper scary to ride. The slacker the better, which is where DJ bikes come in. I have a Trek 820 that's seen a few upgrades and a Giant STP, and the 820's so steep it scared the crap out of me the first time I rode it. If I'm taking a beginner out I give them the STP, even though it's nicer and worth more, and I take the 820.
This is assuming she's a beginner of course, otherwise, well, I love my STP for trail riding, especially when it's wet or there's still snow. So easy to control, not twitchy at all, just stand up and power on and it goes through mud or snow. If you buy a complete bike, check out the tires, they may need to be replaced for slippery stuff since most DJ bikes seem to run slicks.