There is not much more that you can do for her aside from what you're already doing. It is ultimately up to her if she wants to take the steps to address her mental health issues. Withdrawing from others is common when people are depressed so try not to take it personally. If she ever voices an intent to commit suicide or otherwise seriously harm herself, you can call the police if necessary.

I see this is your first post so welcome to PC! I hope you find your time here to be of benefit.