A girl whom follows you and maybe 10 other girls and about 400+ guys, all attractive, follows your man?

I don’t have a problem with her following him, in fact we’re both considering politely asking her if she’d be interested in joining us, however i don’t want to jump the gun and assume she wants my man because she followed him but is it safe to assume she finds him attractive and wouldn’t be too offended by me asking?

How would you go about it? How would you feel if someone asked you to join their threesome?