Jealousy can be a powerful motivator.
Pathological liars don't need a reason, often they can't help themselves.
Could he have rejected her?
I don't think she hates you, I suspect she is terribly envious of your relationship. Maybe she wants what u have?
Maybe she wants it to be just you and her?
Obviously I don't know the answers. But you know her and you know your Husband.

What does your gut tell you?

Have you asked your Husband outright?
Trust your instincts.
All the best,I hope all works out for the the best