I was caught on the hop with periods last year, but luckily the school Sex Ed nurse had given the children a book and some pads/tampons for the previous couple of years. Boots sell a variety of teen lines, so I gave her a variety to try. I also bought her some cheap period pants on Amazon Prime (they just have a waterproof lining) and a little pedal bin and bags for her room.
DD(12) now has a set of Modibodi pants (2 or 3 styles). I reckon she wears those most of the time and switches to towels and the cheaper pants at other times. She is a keen swimmer and, whilst she could apparently train without a tampon, she uses ones with plastic inserts most of the time. The desire to train far outweighed the reluctance to try to insert them.
I think it probably helped that DD is one of the younger ones in her year, so she had plenty of friends who had "been there, done that".
Not so relevant now, but the girls all seem to keep spare tights, pants and pads in their lockers.
I can't imagine she'll be willing to try a moon cup for a while yet.
DD's cycle sorted itself out after about 4 months, but I know some of her friends are still erratic 6 months in. Don't worry.