I didn't comment on her mother saying back in her day a woman who behaved that was was categorized as a slut. I do think that was a bit over the edge on the LW's part, but I think she's looking at it from her perspective.

(My presumption of her perspective) The daughter was deceitful in her representation of the reason for the trip. What else is she being deceitful about, or trying to hide from everyone?

In your example about your friend, I'm betting she was honest with her husband and family about going out with her friends for a bachelorette party? Was her husband with her at the other friend's wedding? If not, did he know she was there?