HUSBAND?!
KIDS?! 
Let me say this before I continue
STEER CLEAR FROM FEELINGS!!!!!!! You're risking
heartbreak if you continue to sink deeper into your crush 
Now I'll address your other issue, about how she's very close to
you online, but acts indifferent to you in person. Online, we are
all protected by a screen, & there's a sense of anonymity,
& distance (i.e. I talk to you, but I'm Not telling you face to
face, so it's less intimidating or confronting, especially for
people who're shy.
Seeing you face to face brings 2 different issues into the picture,
the 1st being that she's disclosing her true identity for the 1st
time. You see her face, & in a way, the sense of privacy is
shattered (for lack of a better word, but Not so drama mama).
2ndly, she's seeing YOU for the 1st time, i.e. now she can put a
face to that faceless individual she has been talking to.
Even after you've met, she may be so used to that cyber realm
whereby there's No face attached to the person she's talking to,
that she'll continue the same routine of talking to you online, but
treating you indifferently in person.
Throw into the above mix, her marriage, husband & kids, &
perhaps that may also explain her indifference towards you. She
might also be trying to prevent herself from falling for you in
person? There're some who think an internet affair doesn't count
because it's Not in reality. Who really understands the human
mind?
FeowFeow