Legally, she is responsible for the actions of her children. If one of her kids took something from a retail store, she wouldn't get away with saying, "I cannot pay you for an item I didn't take." Definitely neg-worthy behaviour IMO.
It astounds me how nasty people get about feedback. I left neutral FB once for a buyer who didn't contact me for 10 days after the auction ended, and even then only after I'd opened a NPB dispute. She did pay, but it was two weeks later. When she read my neutral comment, she tried to retract the positive FB she'd left me, and sent me a barrage of very nasty emails. Hey - the FB system exists for a reason! I have no patience with NO communication. If she'd sent an email saying, I'm sorry but I can't pay for two weeks, I would have been happy to work it out with her.