Well, in my opinion Aquatica has one of the nicest (if not the nicest) kids areas of all the Orlando waterparks. Also Roas Rapids (a fast lazy river) is great and I would think there is no age limit there (though you would have to check on that).
Agreed

(though I think the new sandcastle area at Wet 'N Wild might beat it in size now).
Here are some pics, to give you an idea:
This is the wee kids area:
There are dual wave pools and a HUGE sand beach, great for making sand castles between the rounds of waves:
The traditional lazy river (with tubes) is very relaxing, and takes you past a huge aquarium full of tropical fish:
You can visit the Commerson dolphins (in addition to the large viewing area, the trainers are there several times a day to do demonstrations and answer guest questions:
And like a PP said, Roa's Rapids are the best water feature EVER. Seriously fun. And good for babies right up to seniors. Its a tubeless lazy river with a current that keeps you moving (even my 285 pound DH!). Strap on a lifejacket and go

(yep, even adults....its more fun that way

). We literally spent HOURS there on each of our visits....its that fun.
There is also a family raft ride at the park which I think the OP's DD might still be able to ride at 42".
I think Aquatica is a great park, and offers lots for every age and ever stage (even ride weenies like me

). I would definitely not give it a pass.