Good resources/ways to explain for a not quite understanding mom?

I came out to my mom roughly 4/5 years ago and back then she didn't really understand it at all and still doesn't, despite trying her very best. I'm 16 now and still mostly closeted and afraid to talk about it with her beyond a short conversation now and then because it makes me so nervous trying to talk about it, but staying like this and being stagnant gender-wise is killing me. Is there any ways that I could help explain it to her, or any books on raising a Trans kid that aren't horribly transphobic? She does love a good self-help book lol. I'm just not the best at explaining things when there's not a good way to explain it other than "well that's just how I am".