My friend has become suicidal, what can I do?

I knew she had been sad and on medications because her husband wants a divorce, however I did not realize that her depression had pushed her to the bottom. She has been admitted to the hospital now, and I want to help her. I’m not best-friend-close with her, but I am her only friend left here. The other week I asked her to see a movie/hang out but she wanted to be alone. I feel so awful that I can’t do anything.

Any suggestions?