ah, has a boyfriend. Well, in that case, she's probably just a friendly person, which is a good thing, just evaluate yourself, i assumed, based on the forum this was posted in, that you like her, in the 'like like' kind of way so are you the kind of person who will let that grow out of control just by talking to her and over-fantasizing things? Or can you manage a friendship with a friendly person? (aka, are you the kind of person who, in the past, has mistook acts of friendship as something more because from what little information we have of her i take it she's a friendly person and easy for a naive AS guy to get hung up on).
There's also the possibility she would be interested in a new relationship, in which case I would say stay away, there is always the chance her other relationship is ending and she's open to a new relationship, but I think in those situations more often than not someone like a guy with AS wont pick up on the signs that someone was just looking for a quick romp on the side and fall into the trap mentioned above. If you're willing to risk it, there is no harm in asking a girl out if she's got a boyfriend (the harm is if you've got a girlfriend ), you can just play dumb about noticing the boyfriend thing. I would definitely say to her "can I take you out for some lunch one day" and not "want to meet up for lunch" or something similar. You've gotta word it so that it sounds like you want to take her out somewhere. The latter way can easily be just a friendly lunch and her saying yes wont mean a thing, but if you say to her "can i take you out to..." you'll get an immediate response of "oh, sorry, i've got a boyfriend" if she's in a serious relationship (unless she isnt NT and similarly naive, nothings certain in love and war )
But, i'm guessing she's just a friendly person. So no harm/no foul in talking to her, just dont get hung up over forbidden fruit.
_________________
?It's a sad thing not to have friends, but it is even sadder not to have enemies.? - El Che