Maria, I have several of the Eclipse tanks and absolutely LOVE them. They are a great first tank and perfect for what you are trying to do. You can pick them up on sale at many of the big box pet stores, or look on Craigslist..... I started back into the hobby ten years ago with a Eclipse 12 gallon tank, and still have that one. I've also got the 37 gallon and a 3 gallon Eclipse tank. They are terrific tanks!
The lighting in the 12 would grow anubia, java fern, crypts and anything low light. You could really go to town with that girl theme too. I think it will be adorable -- there are so many cool ornaments out there to decorate with.

Heck, your little fish keeper may even like a few brightly colored plastic plants in addition to the real ones..... I know that's probably taboo to say here, but hey, they don't die, and regular plants don't come in fluorescent colors, LOL....
As for fish, there have been good suggestions made here. The little girl may like to have a look at the local fish store to see what she likes too. Whatever you do, PLEASE DO NOT go with goldfish. They need much more room than a small tank can provide. Once she gets used to this tank, you can always build her a pond for goldfish, LOL.
Anyway, the eclipse is an incredibly simple system. I rinse the filter media pad once a week when I do water changes, and replace the pad once a month. That's it. The only other maintenance is water changes, and any tank would require that once a week anyway.
Good luck. Let us know what you decide on!