Trigger warning* help with bipolar/ postpartum family member!

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Sorry this is so long but I don’t know what to do. My SIL is a sahm of a 3 yr old and a 6 month old. She has struggled with severe depression for 15 years and has been hospitalized twice for it. She recently decided that she was going to stop taking her meds and didn’t tell anyone. She is now in a manic state. I’m not sure if she is bipolar as she hasn’t been formally diagnosed but it seems like it to me. she has been texting me bible verses at 3 am saying god is talking to her and that he has told her about her purpose and that she is special and chosen by home to lead a battle?! Her behavior is over the top excitement, she’s taking a million miles an hour and said that she was told to protect her kids from the evil world at all costs. This shit is terrifying. Her husband isn’t the brightest guy and also doesn’t really believe depression exists . He said she took a nap and has been fine ever since. I asked him to convince her to go to the hospital and to not leave her home with the kids alone. Well he plans on going to work on Monday like normal. My husband tried to go talk to her and she ended up yelling and kicking him out of her house. Sooo... I know since she is an adult I cannot do anything. But do I keep an open line of communication with her? She’s acting like everything is normal and I want to communicate but I don’t want to feed her psychosis. Would you have a welfare check done if she were left alone with two young children all day by herself? ( side note, I am a nurse. I have already spoken with her doctor and also our local mental health outreach) I’m just looking for advice from anyone willing to share if they have gone through something like this.

***Update***

She has cut me off completely but is finally starting to crash. she is physically exhausted from staying up for days at a time. She agreed to let her husband bring her to an inpatient treatment facility, they are there now. The babies are safe with grandparents. The 3 year old today told me “my mommy is really sick, and she cries all the time because she is sick” it’s broke my heart. I havent heard if they are admitting her or not but she’s been there all day so that’s a good sign.