I'd recommend Wind.
Everyone else will force her to have a data plan, though if she's constantly around wifi, she won't really need one.
If you really want to, Wind will let you get a BB on a plain $15 a month plan.
The only catch is, of course, that you have to pay for a phone up front.
In a way, that's better for a student anyway. Gotta learn fast that there's nothing "free" in life and that device you carry around certainly costs a pretty penny - so take care of it!
I'm currently using a Nexus One (love it!)
with $15 voice plan (100 mins/50 text rollover)
and unlimited data $35 (though it's probably overkill.. I'll see what my usage is, probably drop to the $20 one next month-I use wifi at home and at friends')
Smartphone plans tend to be in the $65 range, giving you a couple hundred minutes, usually 500mb of data and couple thousand texts.
With wind you can get 100 mins/unlimited text/500mb data for $40 a month
That should be enough for her needs, unless she's a heavy talker. Even then you'd have to gauge how heavy as it's only $0.10 per minute over the 100.
Usually not enough to warrant unlimited talk for another $20.