How to catch her out so I can confront her?

Well, if you didn't mention that you had a husband, I would have thought you were an immature teenager. Seriously, just leave it all alone and grow up. Walk away from your mother and if she wants to know why, just tell her it all. If the other woman are grown up enough to gossip, then they're grown up enough to reap the consequences of their gossiping. But, enough already. You all sound like little tattle tale kids, I should know, I work with children all day long.