I think I'm going to lose my cool with my depressed friend.
How will that deal with anything?
She needs to know that I'm done dealing with her depression.
You can feel upset and tired. But don't take it out on your friend especially when they're depressed and need your support.
I can't deal with another person who's sad.
It seems like your friend's depression has been difficult for you to cope with. While it's good to help your friends when they're going through hard times, it's also important to take care of your own mental health. Instead of raging at your friend, why not take a break from her and clear your head?