Sea sponges can be a really good transitional product for younger girls. If she does decide to try a menstrual cup, I recommend the smaller size Lunette Cup as it's the smallest and squishiest :)
Menstrual Cups and teens? - Page 2
I'm 16 and I got my period at 13. My mom made me use a period with pads, and another menstrual cycle with tampons after explaining to me the benefits of tampons. She gave me a mooncup. I LOVE MY MOONCUP! It makes me feel clean and lets me do all my sports (track, cross country, volleyball, basketball, soccer, dance, and figure skating), and take my exams without feeling uncomfortable. I don't have the noise of a pad ripping or the smell. I don't have the dryness and the risk of TSS with tampons. I really think that you should tell your daughter that it might break her hymen. I was fine because my hymen was already broken because of all the sports I do. Maybe you should transition her with instead softcups. I personally recommend the Mooncup (UK). It's very environmentally friendly and a lot cheaper than conventional feminine products. You can buy from http://www.mooncup.co.uk/wc.php?u=2772 if you live in the US.
This reads like a cross between a spammy advert for mooncup and a poorly written personal hygiene PSA from the 50's!
I'm 18 and still remember VERY vividly the day I first used a tampon. It freaked me out! It was really gross and bizarre and it hurt!
If someone had handed me a menstrual cup, instead of a tampon, and told me what to do with it, I'd think they were crazy! This would have been my face-----> There was no way I could have been familiar enough with myself to fit that thing up there, no matter how many times I folded it! I had a hard enough time with a tampon!
So maybe just start slow and get her some reusable cloth pads to replace the disposable ones That way you're being green, but not freaking her out. Everyone wins!