My two cents - small potatos and not worth it - paying the bill without further argument is worth the good will.
Every conversation I've had with XW like this, she's countered with something else that she's paid - there's a deep well on each side if you think about it. "Well - I paid for a new jacket" - "Well, I paid for more food last month" - whatever. You don't make headway and it gets silly. And I was pissed off because she's let bills STACK UP until, for example, the propane bill was $600, the phone bill was over $200, etc. It's nothing compared to the other costs though.
My advice - just take care of it and move on. Goodwill. You've got other things to put your emotional energy towards.
