I am saying this as a life long non car owner and bus traveller.
The sheer number of my relatives that have made snarky comments about "you never come to visit", when they are bloody car owners is astounding.
No concept of what takes them fifteen minutes in a car can take me two hours on buses.
A lot of car owners, even ones who previously rode the bus themselves, show zero understanding of the absolute fucking ball ache of bus travel.
Bus- You have to schlep to the bus stop.
Car- Go outside, beep beep, throw bags in back, get in.
Bus- Wait ages for a bus that's either full, late, or doesn't show up at all. Then there's the daydreaming drivers who fail to see you and don't stop at all.
Car- Turn key, check your mirrors, drive off.
Bus- Go on an hour+ long magical mystery tour of local housing estates, industrial estates, hospitals, shopping centres and open countryside because the bus companies have lengthened routes to preposterous levels to save costs and maximise profits. Traffic jams very likely and unavoidable.
Car- Drive for a short while on the most direct route you know, of your own choosing. Traffic jams avoidable with apps, local radio etc.
Bus- Finally reach somewhere a fair distance from where you need to go, get off and walk anything up to half an hour to get there, possibly dragging luggage up and down lumpy gutters and pavements.
Car- Arrive outside destination, walk a few feet, bang, there you are. Luggage is waiting in the car.
You think your MIL is an (insert negative here) for not wanting to go through that more than once in order to spend one hour in the park with your four yrear old daughter.
She can put her luggage in my car for a bit before she has to take it out and lug it back to the bus stop you say. How very generous of you.