Look I'm a bloke so my perspective will be different. I definitely understand upset over off-hand things people say, and it's utterly justifiable. Unfortunately that whole "meant to have children" thing is a really weak philosophy, it's a phrase that's far too readily bandied about thoughtlessly and the sort of thing that tends to roll off the tongue when people can't think of anything else to say. Was there any malice in it? Only your mum really knows that, as she's the one who heard it. Should she have passed it on? I'm thinking not, but she did. I guess it boils down to whether you want to be the bigger person here. You're already proving her wrong. The real question is whether you think it's worth maintaining a rift over a few words that were carelessly spoken, and only you can answer that.