>>57621274In the Serena return episode, Serena literally has May's idol dress available to loan to Chloe at a moment's notice, despite May not being around, so one can imply that they became close friends off-screen. One can maybe assume Lilycove is their "base of operations," since we don't actually know which contest hall Serena, May, and Lisia are watching Ash battle Leon from, and that explains why May would leave her idol dress behind for Serena to loan, but it also suggests that they're close enough for Serena to know that May wouldn't have a problem with Serena letting another girl wear her dress as part of an emergency.
