Usually I don't discuss really sensitive subjects like personal relationship or politics with my parents during eating time. It can potentially get really awkward if we disagree with each other. Though I got really defensive few years back when she mentioned gay marriage and the LGBT issue.
I think it's silly when people said marriage between the same sex is unnatural. There are gay animals out in the nature too so I just rolls me eyes whenever someone says that.
She probably won't think too much into it. My parents get mad at me in the morning than after a nice nap they usually have forgotten it. (At least it seems so) Wish your mum good luck with the interview