In public, I would suggest acting continuously professional and polite. No laughing, giggling, etc. The office is Professional Territory, and I would have a discussion with Maggie about not socializing in Professional Territory. I would actually adopt a more formal method and vocabulary for speaking with her in the office and during meetings. (ie, not "Hey, I have a great idea!" but "I was wondering if we might have an opportunity to suggest some directions for the current project," that kind of thing.)
Senator Edward Kennedy always addressed President John F Kennedy as "Mr. President" when in public. I'm sure that if they met for dinner, he called him Jack or John. Similarly, if you two meet outside of work or chat on the phone at night, be friendly then. But in the office, I would ratchet up the professionalism and always keep things pretty cool and formal.