Sometimes when we are having a bad day, we can behave that way before we even think. She shouldn't try and say her day is worse than yours. But she's not thinking straight, ya know?
I listen to a lot of pastors, preachers, and teachers. I hear again and again that the fastest way to get over our problems is to help someone else. I'm sorry that you are not in the frame of mind to step out of your situation for a bit and help her with hers. But that is really what should be happening. The two of you should help each other look for the bright spots in your lives.
I used to have a friend that was like this, only it was mutual. We would use each other as sounding boards. Eventually, neither of us really talked to each other much. I think we soured what could have been a good relationship by not being or understanding what real friends are for.
The Bible says that friends help each other like iron sharpens iron. There's a process where knives are rubbed on rods and stones to make them sharp. That is somehow supposed to be an illustration of how friends help each other. And yet, rubbing produces heat and that's probably not a comfortable process for the knife..if it had feelings that is. So think of it this way....first you rant with each other, then you help each other count your blessings. I guess.
Defining a good friend and developing a good friend is not an easy task.