My MIL is PSYCHO. Experience or advice appreciated!!

Hey ladies, my MIL is absolutely nuts. She meddles, always thinks she’s right, calls and texts my husband all the time. Complains and gets mad about everything or if anyone disagrees with her. Freaked on him when he said we want to set boundaries. Gets mad if him and his sister don’t text back promptly. I am a 100% convinced she has Narcissitic personality disorder. She’s a liar and I don’t trust her. When things are good everything is fine but at least 1-2 times a month a big blow up happens. Now another one is happening. I’m 5.5 months pregnant and my husband got in a fight with her about what we were naming our child. His sister stood up for us and she got dragged into it now. She texts the most toxic lies. Calls her own daughter a bitch and a cunt. Told my husband she’s not doing the baby shower anymore blah blah. She tries to pit him and his sister against each other. I really don’t want anything to do with her, and I don’t know how to proceed. She’s totally someone who sweeps things under the rug and when things cool off she will try to resume how it was. This has been going on for years and I’m finally fed up. I’ve gone Into mama bear mode. Please share your experiences or tips.