Seven?! If she's seven, she could probably wait a few more years to get her any of those. Seven-year-olds shouldn't be spending all of their time indoors playing games on electronics. Get her something that she likes besides that.
At age seven, I think maybe some of these might be a little too expensive. Doesn't she still like Dolls and stuffed animals still? But if you must, then maybe the iPad would be good for her. Just make sure you change the setting to limit the internet and apps. :)
I would go with some of the cheaper tablets since it might have to absorb a lot of wear and tear. Monitor her access and use the parental controls if they have some on the tablet. Adults must be computer literate for just about every job these days so give her an early start!
All the people with negative comments must not have children. Children as young a 3 use computers in school and as long as the usage is monitored and a net nanny put on there is no reason why your child shouldn't have one. Majority of these can have educational programs installed, so get real people and don't be so critical.