If a player visits her with a friend she will make an assessment of how well the two get along based on your personality types. Marcy can then give advice on these relationships.
Marcy appears to be lonely, as when a player visits on their own Marcy will say the following:
"By the way [Player], have you still not found that special someone?"
"Hohoho...! You aren't being too picky, are you?"
"You don't want to end up like me now, do you?"