This is the "bad thing" that needs to be told to a mom? I always hated hosting sleepover parties becuase there's just not a lot of sleep going on. 11 yr old girls are probably at the worst age - they're so eager to be teens, and to be mischievous, and to stay up all night, etc. So if it's not pixie sticks, it's something else.
Middle school & high school are right around the corner and your friend will be longing for the pixie-stix problems of the 11 yr old. The two girls who brought the candy are either a lot of fun to be with, or really annoying. Your daughter will sort that out over the next few years. Kids go into middle school as kids with playdates scheduled by their parents - and they come out as teens who make their own friends, sometimes to the chagrin of we the parents. This is a good time for dialog and questions about the daughter's opinions of the candy-brining girls & the "bad" behavior. (without details we don't know if the behavior was nudity, twerking, cell-phone pictures and online chat rooms - or - giggly, goofy hairdos & manicures and boy-craziness in the middle of the night.)
This is when moms have to choose their battles. By calling the other girl's moms it will be made into a bigger event than it really is. This is one of those non-events. Dont' sweat the small stuff - and 99% of stuff is small stuff.