If you want to get her anything halfway decent, I would encourage her to keep it inside. Bikes left outside are likely to get stolen even if locked in a rack.
Bikes left outside after a couple years turn to garbage anyway, so I would perhaps suggest a Walmart bike so you aren't out too much. Anything more than a Walmart or comparable used bike is going to be a target.
If she does get something nicer, you certainly want a U-lock. I rarely left my bike locked outside at night, but it did have the cable lock cut one night. It was nothing fancy, just an average department store mountain bike.
That being said, I would suggest a hybrid, they are super useful and great for city/town/multi-use path applications and tend to be a bit easier to pedal than a similarly priced mountain bike.