I'm going to leave my friend when she wouldn't do anything to help herself out of a mental health rut for several months
Why did this make you want to leave your friend?
She's gone too long without asking for help from others
You should not abandon your friend when they are in need. Your friend may just need someone to show some care for them.
Too late.
It is not too late. If you know your friend is suffering, you should reach out to her. Maybe your action towards her will spur her into action for herself.