Okay, my husband just had a cancer diagnosis, so I KNOW that there would be some proof now, not two weeks from now, NOW! There would be a pathology report, a CT scan or s PET scan SOMETHING.
You had every reason to question her, I think anyway. Don't beat yourself up, you did nothing wrong. Let's hope she is lying though and then let's hope she will accept help to find the underlying cause of her deceptive ways. Big hug and good luck. Please keep us posted.