Not blind yet... but I am a woman and I remember being that age. It was not always easy to distinguish between general wetness and blood. In the same way young men get random uncomfortable and unexpected boners, young women get random uncomfortable and unexpected wetness. So knowing if it is menses or vaginal discharge is unclear. However, if she is legally blind, that doesn't mean totally blind. She might be able to check in the bathroom like anyone else that age. However, if she is too blind to tell with a little bathroom check, I would probably go with a sniff test (also in the bathroom). Blood smells metallic. Vaginal discharge smells sort of salty, but not metallic. And with the sniff test I can not emphasize enough the importance of washing hands PRIOR to going to the bathroom, as well as afterward. Vaginas are moist places, that are highly prone infection.

Also, maybe get her and her girl friends to sort of look out for each other. Leaking through one's pants is something that could happen to anyone new to menstruating (or even not so new to it). Oh,the importance of an extra long sweater to cover all embarrassments at that age, and a good friend to let you know you had leaked through your pad, or around it somehow... or a good friend to just discretely check for you in a moment of paranoia to make certain it is all good.. it can not be underestimated. I wish you and your daughter luck. Teenage-hood is so hard.

A little late here too, but thank you so much for the input.