I'm thinking of distancing myself because I'm tired of my best friend's problems
Why do you feel this way?
She's in a bad mood all the time and in my opinion, it became tedious.
It can be good for your own mental health to distance yourself from someone who drains your energy, but make sure you aren't abandoning your friend. When a friend is going through something tough, they need support from their friends and so you should try to listen to their feelings.
I just cannot take it any more.
You shouldn't let others, even family and friends, drag you down with them. It will only hurt both of you.