and I thought I was pig headed (well, I am)

So Nancy's car is not in great shape. Recently she found out she needs brakes and tires very badly. I shopped around a bit for decent tires and brakes for her. I found one of the places we work with that would do it for $600. I know I can find the parts cheaper, but I trust these guys to do quality work and use parts they'd be comfortable putting on their familes cars. That was quite a bit beyond her budget for a couple months. She said she found a place that would do it cheaper. I told her I'd pay for it out of my paycheck and she can pay me back when she gets the money. She said no. I told her she didn't have to pay me back at all. She got mad. I told her I just wanted her and Katie to be safe. Brakes and tires are important safety items. I don't like the idea of going with the cheapest quote you can find. She said she made a decision and it was final, and I should stop being such a chauvanist pig. I know better than to keep pressing my luck at times like that, but I just really hate the idea of people I care about that much getting into a car with bad tires and brakes. I worry about them.