I'm not a mom either, but if the girl wants to use tampons, then she should use them. When i first started menstruating, i was scared of using tampons so i used pads. When i first wore a pad i cried because it felt like a diaper. Soon after, i began to wear tampons and they were much more comfortable.
Nowadays they're making really skinny tampons, aimed to help younger girls get more comfortable with the idea of using them. The main brands such as Playtex and Tampax both make a slim fitting tampon. Also, one with a plastic applicator will make it easier and (in my opinion) more comfortable to insert. Good luck.