"The Mini Bow 2.5™, 2 1/2-Gallon Acrylic Little LAGOON™ Starter Aquarium Kit Includes:
A crystal seamless acrylic bow-front tank.
UL Listed, full incandescent hood with 15 watt bulb included. " --from the All-Glass Aquarium website. I assume this is what she has?
If so, she should have no problem growing one or a few small plants. I'd try the Anacharis first, very cheap at the lfs, grows very well, and gets al of it's nutrients from the water (as opposed to a root feeding plant). That will help greatly in reucing nitrates, nitrites, and ammonia.
Also, it's a stem plant, if/when it gets too big, just trim off the ends and replant the best looking part of the plant.