Gosh, that is really frustrating. :( You most definitely did do the right thing, and it sucks that it’s having such a seemingly negative outcome so far. I honestly don’t understand why her mother would be mad at you - I know that if it were me in her position, I would be really grateful that you reached out to help my child at all. You couldn’t have been expected to tell someone about it right away, because I’m guessing that your friend didn’t want you to tell anyone - which makes deciding to “betray” that trust and say something a difficult thing to do. And I put “betray” in quotes like that, because even if she wanted you to keep it a secret and is mad now, you did what is ultimately best. That is not something to feel bad about. A mediocre friend would’ve said nothing, because they didn’t want to risk the friendship. But you took that risk and did what you had to do for her to get help. You risked losing your relationship with someone close to you in order to give them a shot at a better life, and I think that actually makes you a really amazing person. Hopefully, she will start to see that soon, and you can continue to be friends (and to be honest, I have faith that it’ll turn out that way in the end). And even if that doesn’t happen, you still did the right thing, you truly did. As far as her mom getting mad that you told a teacher/got the school involved, that’s also ridiculous. For one, it’s clear that she herself wasn’t the best person to go to. Also, teachers/adults at school are supposed to be adults you can go to - many resources for things like this recommend that, because then they have to reach out to the parent (which takes the pressure off you/whoever has the problem), or alert the school counselor and such. Again, you did the right thing. And even though it may not feel like you did anything to help right now, you did. You did everything I would hope someone’s friend would do for them in this situation, and ultimately, I really do believe it will pay off. It’s likely that this will lead to your friend getting professional help, and that can be the first step towards recovery for a lot of people.
I can’t make any promises about what will happen, but I can promise that I think you did the best thing you could’ve done. I hope things get better for both of you from here. <3