Canada

I don't think you're going to find something that fully meets your needs.

Sprint, Verizon, and probably others offer plan add-ons to make calling to Canada pretty cheap, but calling *from* Canada will add up.

Beware that on a family plan mobile to mobile will probably not be usable if either party is off-network, which would be the case with one person in the US and the other in Canada. With Sprint it would count minutes since it's off network. I very much doubt that would be different for the other carriers, but reps from other carriers might be able to chime in to confirm or clarify.

If she was just there for a few weeks or so then it would be better to stay on the US carrier with you, but the international roaming costs would quickly make that not worth it.

Your best bet will probably be to keep your family plan you current have or that best suits the family members in the US, and then have your daughter get a prepaid or postpaid plan from a Canadian carrier. For all of you, it would be beneficial to get add-ons to call Canada or call America in her case.

If I were to be a student out of the country, I'd get a prepaid phone in that country, but I'd also get a Skype or VOIP "home phone." I'd make the long or regular calls from the VOIP phone in my dorm, and only sparingly use the mobile to call home.