What are your thoughts on this? My mother-in-law has hot flashes, so I'm planning to turn up the thermostat when she visits.
Did she do something to make you want her to be uncomfortable?
My husband is sick of her. She annoys the shit out of him.
It's really petty to mess with the thermostat just to make your Mother-in-Law uncomfortable. If she annoys you two that much you should just tell her directly, otherwise you should be accommodating her instead of making her uncomfortable. Being passive aggressive isn't going to solve the problem, it's honestly just going to make it worse.
It's not being petty. It's a scheme to make her leave.
If you don't want your mother-in-law to stay in your home, you should respectfully let her know about hotel options nearby. However, being passive aggressive will not help with this issue.