Huge backstory to this one and don't want to dripfeed
Myself and dh get on well with FIL but MIL is basically an awful person (although FIL enables her for an "easy life" which also winds me up!). She basically has no friends left and dh's siblings have very little to do with her anymore. By the sounds of it, when they were growing up children were very much an inconvenience to her (unless she was showing off one of their achievements) and she made no secret of the fact that they were to stay out of her way (to the point where basically they would come home from school, go to their rooms, emerge for dinner when FIL came home and then go back to their room so they didn't have to interact with her). Hearing stories, I do wonder whether she was suffering PND or similar but can't say as I wasn't there.
DH & I have been together for nearly 15yrs. She is quite manipulative in that she tries to be friendly with me at some points but have heard her talking about me behind my back or she will openly criticise me to my face, on one occasion telling me that I wasn't good enough for her son and that I am not welcome in her family. Following this, I tried to avoid her but would be civil when meeting up at family events, then she started referring to me as her daughter-in-law so figured that she may have finally accepted me and tried to get past this.
When dh and I announced our engagement, she stepped it up a gear and criticised all our plans (even going so far as to talk about it behind our back and cancel some things that we had planned, luckily we found out and was able to sort it out) which prompted dh to have it out with her and she actually did turn it around at this point as apologised and was "good" for quite a while (prior to dh's talk, he did the same as his df and pretended it wasn't happening even though it upset him a lot; he says when we were getting married he realised he had to step up and be there for me even if this meant going a against the grain with his family).
However, we have now had a baby and she is openly critical about our parenting choices (Blw instead of purée food, having a bedtime routine- not set in stone but always read/brush teeth/bottle before bed, etc.). When dh tries to be firm and say that it's our choice as parents to do these things, she then gets upset and says she was only joking and what a wonderful job we are doing.
As my dh has picked her up so many times on this, both at the time of doing it and having more serious talks with her (where he has said that if she continues we will be considering low/no contact with her), she now alternates between criticising me or completely ignoring me when my dh is not in the room and then acting normally when he returns. As a result, I now make excuses to not be in the room with her (e.g. Making drinks while dh stays with them, making food for dc, even ironing in another room). She has told other family members (aunties/uncles/grandparents) that I am being rude and making them feel unwelcome and I am now being ignored by other family members. We have tried not to get into it with extended family as they all love a good gossip and don't feel like we should have to defend ourselves when they all know what mil is like.
Although we have threatened LC/NC, I don't know if we actually want to follow through as although MIL is awful, FIL is a very nice man and I don't want dc to not have a relationship with their grandparents. I also suspect that she would influence other family members to cut contact with us if we were to cut contact with her. I only have a few immediate family members in this country (the rest are spread across the world) so I feel like dc will miss out on having family relationships if we were to go NC.
So basically, WIBU to hide upstairs (or go out) when PIL visit, so they don't know I'm there. Then She can't say I'm being rude by busying myself in another room and I don't have to put up with her being rude to me.
TLDR; MIL is horrible, WIBU to hide in my own house to avoid having to see her.