Well actually I didn't, I noticed that due to rail strikes etc she wouldn't actually be able to get a train home after Christmas. She lives on the other side of the country so would have to take the train. She could get a train to us on Christmas Eve but there are no return trains. I pointed this out to DH, he didn't seem bothered and said that was fine (!).
Long story short, DH isn't close to her and has been LC for years. Recently though he's had a sudden enthusiasm to introduce her to our DC so she came for a weekend a couple of weeks ago. He made no effort to host her so I was left sitting on the sofa with her awkwardly. She's a socially awkward and strange person, DH doesn't enjoy spending time with her and I get anxious having to host her on my own.
I was getting my head around hosting her for 3-5 days over Christmas, but I will definitely not get my head around having her here for an indefinite period. DH wouldn't do anything to inform her about the trains, didn't want to upset her, so I had to message her.
As much as I wasn't looking forward to hosting her over Christmas, I also didn't want to leave to find out that she couldn't visit only days before Christmas. At least now she has time to make alternative plans. No FIL in the picture, but we haven't actually spent Christmas with her for about 7-8 years I think, so she has friends and family that she usually spends time with.
So I told MIL that trains were an issue due to strikes etc and it would be better if we saw her after Christmas, she sent a message back to say that she agreed but now DH is fuming and refusing to speak to me. He says I'm controlling and won't allow his family to visit...