I have a biocube, 29g and I love mine. I have had it for a couple years and it's pretty simple to run. Like stated above the stock lights are not strong enough for ALL coral but are pretty good for the majority of them.
I've had anywhere from 4 to 7 fish in it at a time, all depends on the fish. But for sure you can keep a pair of clowns and maybe a couple other smaller fish. It's easy to maintain as well.
The only problem I see with it is that your mom will love it so much she may want a bigger tank! LOL