What should I do?

Try the truth.

As a footnote if is normally not a good idea to get involved with someone at work as it can end up bitting you in the rear end in many ways.

Of course it work out well for Bill Gate.

She had to ask for your height? Couldn’t she tell there was only two inches difference in bed?

She might be vertically and/or horizontally dyslexic.

Considering she tossed you on the scrap heap because of an inch or two difference in height (so small she couldn't tell until she asked you) - do you really want someone who treats men that way in general?

Considering she then went to another guy at work, knowing you liked her and screwed him - do you really admire people who do that sort of thing to you (or anyone)?

Considering what she thinks of other peoples marriages - do you think she'd stay faithful to you?

Considering she's only choosing you as a fallback, are you prepared to accept that position?

Not too harmful if he is only looking for a fast roll in the hay but not if he wish to find someone for a more meaningful relationship.

THIS OFFICE ROMANCE IS NOT A GOOD IDEA SHE HAS A REPITATION ALREADY FIND LOVE OUTSIDE

Forget about her, it will never work, and if it did it wont be for long

Forget about her, you're too small.

Tell her you are not interested in her "that way" anymore. And say it with a smile. ('cause you are so glad not to have gotten involved with a girl who is so superficial that she considered height important, then chose a married loser over you)

She thinks you have absolutely no self esteem. Avoid her and show her how wrong she is. She will respect you for that.