I spoke to my neighbour over the back from me about a year ago to see if she'd be willing to half in for the back fence (fence at back of her garden, fence at back of ours) and she said yes that would be fine and to give her a quote when we had it.
Then Covid happened so we have just gotten round to it. I went over to give her quote (150 each) the other night. She then said that actually the fence at the back was our priority to fix and pay for as the posts are on her side of the garden! 
I said I don't think that's how it works and she said that the two fences at the left and right of her garden were her responsibility as the posts were in the neighbours garden therefore she gets the 'pretty' side of the fence meaning it's her responsibility. But as the fence at the back of the garden posts are in her garden and we get the 'pretty' side of the fence it is our responsibility.
She said she can't just go around halfing in for the upkeep of other peoples things and when the time comes she won't ask her neighbours to on either side either.
AIBU to think this is absolutely bonkers? Trying to find out if there's anything I can do to ensure she pays half as that is not how it works. She has a responsibility as well as we do.