She wasn't pregnant. There was no baby.
She is playing mind games with you. Its sick, I know, but some women think this is how to get a man to bend to their whims.
I will repeat: THERE IS NO CHILD. If their had been, and she'd miscarried, like she says, she would have been in the hospital, she'd have had to have a surgery called a D&C.
And you know what else? ALL her friends and her family would know about the baby. The first thing a woman (ANY WOMAN) does is tell her best friends and family - the fact that no one knew she was pregnant and there was never any proof of it tells you all you need to know.
For your own sake you should stop any relationship with her. Find someone who will not be so deceitful.
Good luck!