I apologise in advance for the length, because I fear this might turn a bit ranty.
MIL drives me insane. She is deeply racist and xenophobic, which comes out enough when sober, but she also drinks heavily which leads to slurred rants on immigrants (one memorable quote "Those asylum seekers don't need them food vouchers, because I've seen them in the supermarket, and they're all fat"). She has at least mostly stopped drinking till she throws up now, but I still haven't forgiven her for the times i've had to clean her spattered vomit up from the bathroom, including once when I got up to feed dd I the night and found the sink covered in dried on sick.
She is the messiest, dirtiest adult i've ever met. Making a cup of tea invariably involves scattering tea and milk all over the kithen and leaving all the cupboard doors open. She leaves little bits of used tissue all over the house (including by the toilet). When she leaves her bed is usually full of mud and crumbs and although obviously I wash the bedding I always feel like I want to fumigate the room before ds goes back in.
She has massive social problems, to the point where she can't actually hold a conversation. She just can't take in what the other person is saying and uses the time they are talking to decide what she's going to say next, which is usually unrelated. With more than one person this is worse - she just can't follow the conversation in any way so over most dinners just gets increasingly drunk and loudly talks over the top of everyone (see rants about immigrants above). This also means she can't interact with the dc at all and they both get increasingly frustrated with each other.
She usually comes to stay for 5 days at a time. This is bad enough. She always comes for Christmas as she is a widow and dh is an only child (and she's fallen out with everyone else she's ever known). That's fine. However, yesterday she announced that she's booked her tickets (totally undiscussed with us) and is coming for a week. I genuinely think I might kill her if she's here that long. So after all that, AIBU to think up an excuse and tell her she can't stay that long? Or just fucking tell her?!