Accept that, do some banishing rituals on it, try some of the stuff listed here:
it really sucks, you’ve been let down by someone YOU were helping UP. You deserve to acknowledge that.
Then, though, it’s time to put your game-face on and do “wanted nothing but the best” for yourself.
Stop looking for any more lame ducks to help and expecting they will be grateful to you forever, they usually won’t - they’ll use you then move on. It’s not healthy and it just makes you identify with this whole sad vibe, being one of life’s victim/rescuer folks.
i’m not being mean but that’s coming all through your post right now, and being rejected like this as a friend is just going to add to it unless you ID that shit and sort it out.
Barest minimum, read this, before you try to drag her back down into loserdom so you can feel better:
Ask this excellent and magnificent beast how you can sort yourself out, become happy, and get the great powerful friends you deserve:
if she’s in your age group, she’s really just a kid, one day you may be a parent or mentor to younger people and you’ll realise this - that stupid arrogant kids fuck things up, and crippling them for life improves NOTHING for the world, or even for you, once you get 10, 20, 30 years on from where you are - and those years will last a lot longer, trust me.
So I’m not saying don’t do what you want to do because morals, I am saying, work on yourself first, grow past this, and become the kind of person who attracts quality friends. 