We have 3 kids and a 3 bedroom house. Lots of kids, toys and stuff! Rejig of rooms when she stays, blow up beds etc.
About 4 houses down is an AirBnB, £26 per night. Really nice lady runs / owns it. Is it unreasonable to suggest she stops there in future? MIL doesn't visit often, only 3 times a year for a 4 days, no FIL on the scene.