I can sympathise having met a few bullies here too. For me it is about letting go of my knee-jerk reaction which tells me I am RIGHT.

Went through the same thing yesterday with my current 'boss' who was determined to believe that the small bugs all over my feet were not fleas... which they were! I was making myself more and more stressed by trying to prove what I believed and the more I pushed, the more she pushed back. Only when I let go and told her she was right could we continue with our duties without any further stress. Though i now have small bites all over my legs! haha. The price of humility!

Your mother sounds like a wise woman :)