I'm going to tell my depressed friend that she's toxic
It's because you don't want her to be around you, right?
Exactly she keeps ruining my mood.
I understand that your friend makes you feel unhappy. You should let her know how you feel even though she is going through a hard time. Make sure you are polite though, because you don't want to cause her depression to worsen.
That's true. She has helped me before when I felt bad
I hope you can have a productive conversation with her. If you think she might be open you can try to ask her to see a therapist.