While I agree livebearers are definitely a better choice, especially when she has a guppy already, water changes are a must anyway. Pea puffers rarely eat snails. They don't have the teeth that other puffers do, so they don't need the snails to keep them down. My dwarf puffer tank was infested with ramshorns and it didn't touch them. Pea puffers are very easy to care for and eat a wide variety of foods. Since they can fight if the tank isn't heavily planted, I'd only do one though. Either way, I'm afraid the tank may fail though if she's not ready to do the maintenance. I agree something very hardy and low maintenance is the best way to go, but I'm not suggesting the neglet of any fish.