You are fully allowed to reject anyone's advances. It's your responsibility to yourself to make decisions you feel are right.

It's very important you understand that her actions were not a result of you not wanting to go out with her, and they're not even a result of her having "a lot going on." Her suicide attempt was a symptom of a drastic mental health crisis for which she needs immediate professional help, and that is something far beyond what you're responsible for or equipped to do. It is also not something that would have been fixed or helped in any way had you even decided differently and gone out with her.

The best you can do is hope she gets the help she needs. Consider contacting local suicide-prevention organizations for further advice if you want.

You are not responsible for the actions of others.

Are y'all from the same couple-pair? lmao

Did the rejection negatively affect her mental state, which in turn pushed her towards acting on dark thoughts? Probably.

Did you cause her hanging attempt? No, the hanging attempt was caused by her tying a belt around her neck and attempting to hang herself.

You are not responsible for the actions of others (in most cases).

It's not your fault you're straight, you don't get to choose what you're attracted to.

If your friend's explanation is that she had a lot going on, it's probably her overall mental health that's the issue.

Being rejected romantically is sad, but a normal part of everyday life, and not enough to make an otherwise healthy person react in this way.

You can be there for her without being the person she wishes you were. Be her friend. Do what a friend would, and she will heal and you won't have this on your mind.