My first post, so please be kind.......
My partner has just cast up to me that I "never" support her in arguments/discussions with our 15 year old daughter whenever they are arguing (this isn't a constant thing, normal parent/teenager stuff n- clothes, bed-time, eating etc). However, on the occasions where I've interceded to support her, she then tells me off for not letting her deal with it, thereby under-mining her ability and authority.
I feel I just can't do the right thing either way. 
Pointers and suggestions most welcome!