My best friend is severely depressed. She feels like she was made to destroy everything, and I get the idea that she sometimes wants to kill herself. Please, what can I do to let her know she's important and she's loved?

Has she tried talking to a therapist?

There really isn't anything you personally can do to help depression :/ You can still be there for her, yes, that's great, but she has to make changes for herself :/ You alone can't really save anyone.. I suggest her getting professional help.

You can be a supportive friend, but she has to want help before anyone can help her.