So you've told her this is a bad time ( multiple times) she's completely ignoring you, she went to the station early (can't go home now...) and she's on the way.
This probably won't work but is there any way that you can intercept her at the train station when she arrives and bring her right to a hotel in town? No discussion, if she's staying she's staying at a hotel. (Ideally, not to a hotel in town, ideally you tell her to go right back home as was mentioned in the post of all mine.)
Now you know the very first thing she's going to do is get a train or a taxi to your house, and this is a terrible time because your husband is going through the raw loss of his father, yes it's been a year but that doesn't matter. The first anniversary is exceptionally difficult, the date is really really hard and he's going through a lot right now....
I'd almost say is it worth bundling up your whole family and you guys going away for a few days? Yeah I know that sounds crazy, fleeing your house out of necessity because your mother has invited herself to visit but you told her not to come.
Even just being away for a day or two might be very helpful to your husband, spending time with his family (you and the kids), his direct lineage from his father, maybe doing something that his dad would have enjoyed, like if his dad like walking in nature or if his dad likes museums or if his dad liked a certain kind of restaurant, maybe doing those things to honor the memory of his dad and because you guys are family you can do it all together with him? But not with your mom. He already doesn't like her and she's being disrespectful.
Your mom's going to be exceptionally unhappy either way, because if she comes to visit and no one's being extremely hospitable towards her because she's not supposed to be there, and your husband's locked himself in the room, well let's just say it's going to be a bad visit. Can it be much worse if you guys say sorry, we have plans, we're not going to be home....
I'm really sorry for the situation you found yourself in, but right now I would say if you can, be supportive of your husband.
Grief is a unique experience for everyone but I found the days leading up to the anniversary of the one year of passing to be exceptionally stressful.
(Edited for spelling)