I'm MtF but, I've been following this company: http://www.flavnt.com/bareskin-swim-top/ since their kickstarter. I'm not sure if they are a better binder than other brands, but they sorta created their product from scratch since they weren't satisfied with the binder options available.

As others have stated blockers are the drugs that prevent natural puberty from taking its course. This is supposed to be a huge help for trans teens. I think Hormone Replacement Therapy (HRT) would start at 16 or later from what I've read. I started transition later so I don't have first hand experience with taking hormones at a young age.

Some other reading might include: 1. Letters to My Brothers: https://www.amazon.com/Letters-My-Brothers-Jamison-Green-ebook/dp/B00466H99O - this inspired its companion Letters For My Sisters which I loved. It is a bunch of essays from trans men giving advice or writing to their former selves. 2. Trans Bodies Trans Selves: https://www.amazon.com/Trans-Bodies-Selves-Transgender-Community/dp/0199325359 - This is sort of a good academic base of knowledge written and compiled by trans people with a lot of first person asides from trans people speaking about their personal experience. 3. Girl Sex 101 : http://girlsex101.com/product/girl-sex-101-paperback/ - Not sure her age, but this is specifically for her if she is into women. Specifically they have a lot of inclusion of trans men and women on topics of dating, knowing your body, communicating, and anatomy. It is very approachable and quite the fun read while still being very accurate and informative.

It is super important that you find your own support as your journey is a bit different than your child's. Thanks for a being a responsible parent listening to and believing your child as well as reaching out for help.