My friend is quite complex: clever, kind, generous with her time, supportive, discrete, underemployed, does not do nuance and thin skinned.
She and I are part of a wider friendship group which is how we met. We've been friends for years but every so often she will take offence at something that someone else said or did and she expects me to side with her. Staying neutral isn't an option, apparently.
I make mistakes too. Sometimes, I can see them but other times, I really can't see what she's upset about. No amount of reassurance or explanation will calm her down and she has lots of spare time to brood about it, which doesn't help.
I feel like I am walking on eggshells all the time, and when she takes offence at me, she will not agree to differ or leave it alone. It goes on for hours and I feel I can't escape, nor reason with her. It always ruins my day and leaves me feeling battered and bruised.
What should I do about it?