Weird AF? , title too short

I saw her April was a year ago, we went to where she was staying because it had been several weeks since we last heard. She refused to come out, I insisted. She got all bent out of shape and a week later she came her to get more of her stuff out of the house.
The last two messages were ignored. The last phone calls, same. She has talked to my niece once in the last few months and possible my sister. She blocked her mom on fb but occasionally unblocks her for a few hours, we figure it's to see if anything has been said about her. She's cut us, her brother, and her grandparents completely off. She is still "friends" on fb with my sister, a niece, and some distant cousins and they do regularly see her fb and screenshot things they think we may want/need to see.

Last April she was living next to a major highway and it would have been possible to ride by and see if the SIL was there, but then they moved to an apartment over a garage is someone's back yard which is way off the road and you can't see anything without driving up into the yard. The property owners are an older couple and I know them well enough to know if they saw anything unusual they would have gotten word to us. My wife thought about riding up there Memorial day weekend in hopes the SIL would be working but didn't want to have to deal with him or risk upsetting the daughter ( we figure she must be about 8 months now.) If we had any clue that he went to the beach and left her home alone we might have rethought that.
AFAIK they are still in contact with his parents but it is a love/hate relationship. They are also in contact with his sister, and I believe if she was aware of anything major she would have contacted my son (they've been close friends for years, I know they went out with friends a month or two back.).
My son and the son of the property owner where they are staying are friends so there's that, and I think if anything major was going on we would hear. This all seems to be a recent development, and getting my son involved may at least get us some clues as to what is going on.
I'm reasonably sure that when this all started the problem was him and not her but she chose to play along. Now it seems he has somehow brainwashed her into believing "we" are the enemy. There's been weird fb post that have been screenshot and sent to us. The last one I remember the property owners son contacted my son with "what did she mean by that?. and we had to fill in details of a story my son wasn't aware of (read ex boyfriend, 10% truth/90% BS).

Part of me wishes they have split and maybe this could be the catalyst that causes her to open her eyes and see she is being played. Probably just wishful thinking.

Your daughter might be in a bad situation with a guy like that. What attempts have you made to see her?