Here's one more theory: Our memory isn't as good as we think. There have been studies to validate this. My sister and I have compared notes and found that things we thought happened either didn't, or happened to the other person. I had a memory of my father throwing a coffee table out the door that I "discovered" during therapy, which proved my dad was trying to protect me after I fell on it and broke the glass. It turned out to have happened to my sister, and it was a mattress that he was struggling to get out the door at a different time.

There's the possibility that your mother never said that.