I'm with Ricochet on this one. This is a proactive stance instead of a reactive one and taking a proactive step to prevent these kinds of incidents is the right thing to do.
I would love to take my girlfriend out to play with me but probably not with those guys. Not because they'd hit on her or anything but IMO the game dynamics aren't conductive to couples. Even though I'm not generally a totally overly protective helicopter boyfriend (really, she can handle things on her own) it doesn't mean that I won't be overly protective if she gets hurt or close to getting hurt.
With MTB, I wouldn't want to see her get hurt but there's really only yourself or equipment failure to blame if you lowside or drop or whatever (and it's usually either yourself overstretching your limits or you not maintaining your equipment leading to failure). With airsoft it's a different dynamic, there's the factor of the other person, yourself, and equipment failure. The last two are alright but add the other person factor into it and you have something that can blow up in your face quite easily because it's easy to blame someone else rather than your own self or equipment failure.
On the other hand however, I would join her to short day skirmishes at some of the other "for fun" clubs/groups.
Also @ Ricochet: I don't know if you heard, but I went out to play last week and I'm now "medium nip" in the Swat-21 group