You had to even ask? This sounds like the person who gets 6 of her friends together for a 3 hour lunch at a nice restaurant and tries to leave coins as a tip. I ALWAYS added the 15% on large groups of women after losing huge amounts at lunches as they camped on my tables drinking coffee and splitting dishes.
Tell it! I've noticed that in large groups, there's a always a bad apple or three that will chip in only for their own entree, withhold on their drink ("I only had water!") and tax ("uhhh... and what would that be?"), and weasel out of the tip, too, if they can.