Other woman claiming to be pregnant
Your situation sounds very stressful and emotionally overwhelming. You must be so over this issue. Have you thought about going to local police to report this person. I would be looking at a restraining order and closing down or blocking this person from all forms of social media.
Then from there, anytime this person tries to engage with your husband, at least this way, you just need to contact the Police and then they handle the issue directly with her. If she were to continue to stalk you and your husband (theoretically, since she is stalking your husband, she is legally indirectly abusing you in that aspect).
I have lawful knowledge in this area. You must also be aware that you or your Husband must not make contact with this person to appear to them that you both do not exist so that she can deal with her little fantasy.