What excuses could I use to gracefully back out of a trip that my mother-in-law has invited herself on?

Have you ever suspected that petrol from a filling station damaged your vehicle?
Should pride be based on your own rules or on what society expects?
Why do people say narcissists have a shame wound if they don't seem to have any moral standards for themselves?
What’s the connection between a narcissist’s fragile ego and their need for constant validation?