Don’t worry: there’s plenty to do in Universal. I have to mention this all the time: Universal is Disney’s competitor for a good reason: they have a lot to offer.
If you’re staying on US property then you will get front of the line passes and be able to do as many rides as you like. The crowds that week should be very high due to both spring break and the opening of Harry Potter, but if you are holding that card, you’re golden.
What I always did with my kids was replay any movies that are featured in the parks/rides so they got the full excitement out of seeing them come to light.
With a 7 year old girl, the big rides are probably out (some little girls love them, so who knows?), but there are kid’s areas in both of the parks.
I think Mardi Gras will still be going on when you’re there. That’s wonderful. A tiny taste fo the real thing with a terrific parade.
City Walk has some terrific themed restaurants. Be sure to check those out.
And don’t miss The Horror Make Up Show. Trust me. It’s nothing like what it sounds like. It’s for all ages and it’s funny.