maybe she is pining for the high school days in general then when he was more her little boy IYKWIM? Him getting married might have triggered off all this stuff for her about him growing up or becoming an adult and not needing her anymore (in that marriage is still such a rite of passage for many people). I dunno, I would have thought most people do want their kids to be happy but maybe she was thinking more of her own feelings.

ETA - I'm glad they each didn't observe her rude behaviour. Lets hope it was a once off in the context of being all emotional and she just forgot herself.