There are smaller tampons for teens but if she bleeds through maxi's or overnights, they are not going to work either. Overlapping pads is not a good idea because of the plastic layers in them. Incontinence pads and panties might work better for her.
The answer might just be for her to change whatever she use more regularly during the day and use a different product at night.
Menstrual cups may also work for her although it may be difficult for her to find one small enough. These can normally take much more flow than any other menstrual product and can stay in for much longer.
It might also be worth her while to use hormonal birth control to regulate her periods. It is not something that should be done lightly but if she is missing school, it is a major problem in her life.
Best of luck!!