Using a cup from menarche?

Hi everyone! I'm a dad with a pre-teen. I know eventually she'll get her period and this may sound weird, but I really want her to use a menstrual cup/cloth pads. She swims like everyday and we live somewhere costal so internal protection is a must. (She should at least have the option.) So here's my first question: How practical is it that a teen use a menstrual cup for her first periods? I mean I can't help her in that department, and I don't want to resort to tampons. (The health concerns/enviornmental impact do it for me.)

Also, How should I approach this stuff with her? We're both comfortable talking about this stuff, but I'm guessing all her friends use tampons/pads..

Also, is there a natural soap she could wash her cup with? (Besides Dr. Bronner's its very expensive where I live.)
Any advice you could give me would help. (Especially if you're a teen/parent.)