I think the wave pool may be the only thing you may have any problems with ... I am not a swimmer, so I don't do that. I did the first time we were there, hanging nearer the shore; however, if you get knocked down back there you can get some nasty scrapes from the roughened cement bottom. The rest of my family does the wave pool but will go up nearer the front -- they love it!
I have been able to do everything else at TL as a non-swimmer so I think you will be fine and will have a great time.
Some suggestions:
> Bring your own towels
> Be at the entrance at least 20-30 min prior to park opening
> Know where you plan to find a seat and head directly there as good seating will go fast (don't stop to get a locker, etc - you can go back later once you secure seating - items should be fine; however, recommend a locker for those "can't afford to lose" items)
> We like to get seats near shade, so that we have some relief from the sun at some point in the day
> Make sure you pick a "landmark" near your seating so that it is easier for you and your niece to find upon return
> Discuss what your niece should do if she should get separated from you or "lost" (CM's will be dressed in red shorts/swimsuits with name badge)
> Bring a small cooler - No glass or alcohol allowed (they will check at entrance for these items) - with beverages, sandwiches, snacks ... the food is expensive and the lines can be quite long
Use lots of sunscreen and have a great time!
