Ok op here what you do- listen carefully...
The night before your MIL gets here, you go down to your local Zoo, break in under cover of darkness- steal the biggest Orangutan you can fucking find (you can lure them outta there once you have the cage open with Doritos, just make sure they are ORIGINAL flavour, or you don't wanna know what will happen...)
Get the Orangutan into your house, don't ask me how to get DH on board with this, thats not my problem, you just gotta get him to accept the Orangutan is part of the happy family unit now.
So once your MIL gets here, you act like everything is totally normal. Little does she know you have a brand new house guest sharing her room. When you show her in, ignore the Orangutan sitting on her bed until she brings it up. Then casually explain that he is staying here a few weeks (he's just dropped out of uni and needs to get his head straight or some shit like that.)
Wherever your MIL goes, the Orangutan goes. make this clear to her from the beginning. He shares her toiletries, he uses her hairbrush, he wears her clothes and underwear. When you make dinner, he sits next to her at the table (non negotiable) and encourage her to make polite conversation.
You treat the Orangutan like one of the family; he goes out on trips with you, your DC skip merrily down the road holding hands with him. If your MIL dares to question things, just tell her shes really out of order to ask- hes going through a rough time now and just needs the support of your loving family.
If she manages to last the whole trip, make sure that when shes leaving, you dress the Orangutan up in your DH's best shirt and tie and stand there at the front door holding his hand and fucking waving as she drives away. A few days after the visit make sure you text her to say your other house guest really enjoyed her visit and he can't friggin' wait for her to come back and stay.
You'll never see her again. AND you have your furry orange friend to thank for that.