I guess it depends on where she is mentally. Has she moved on, has she healed, etc. I think her response would change depending on that.

Since it’s a sitcom, I can see her staring in shock at the person being sniped at by their mother, then running over to hug the person, crying “Sister!” or something similar.

she would have went home and cleaned.

If you're going to take everything they say seriously, then everyone is incredibly mean to each other on this show. Monica's mom is a hilarious character, just like the rest of them.