Girls do this also when they get approached by guys all the time, shes thinking why I am going to let this guy in with me is he any better than the idiotic guys ive come across.
They test us by throwing in these bitch shields, its up to us to form our own strong reactions in the correct mannor because that's what shes looking for.
I had this happen to me on the weekend, its the third time its happened to me in the past 3 months and it all happens as soon as you introduce yourself shake her hand etc.
She says to me " I am actually married " and without dropping my expression on my face keeping it natural I say " oh wow that's great" pause.
Then I will ask her a few questions I want to catch her out, because for one thing ive still got my arm comfortably around her and she isn't pulling away.
I say " so whats his name" she replies within 10 seconds " james " I go on to say " cool are you happy" ?
She replies with a slow yeah.
I then say " well thanks for telling me anyway its good to know as I was about to make a move on you " she smiles leans in kisses me on the neck, boom I am in I put my hand gently on her neck and move in for the hook up
The other thing is I knew the vibes were there too so I can be comfortable around her and make my move when it feels right.
If you get a response that is cold don't stuff around with her for too long, shes not worth the time and effort move onto another potential hottie.