What fish has she got? How long are the lights left on every day? Is the tank near a window? There's a few things you can do. Firstly, cut down on the amount of time the lights are on (6hrs daily if its really bad, 8hrs max), or, get an algae eater. I got me a pair of bristlenose plecos in mine and they cleaned the tank top to bottom in just two days. They do a stunning job keeping it looking clean and clear. Obviously adding more fish depends on how stocked the tank currently is. Hope that helps.