Kind of sounds like you need to use group theory.

Could you just walk in there and ask all four of them if they want to grab lunch? Take control of the situation you know? Your a social person so it shouldn't be too hard to entertain two dudes and a lady at a lunch. Plus in there you can set yourself up for next encounters.

Or you could approach her solo and just ask if she wants to get out of here. She'll either say yes, no, later, or maybe later. Maybe later is in my opinion is worse than a straight up no. No matter the response your response should just be Ok with a shrug.