There will always be cases of collateral damage. You won’t be able to safe the climate in such a big and complex society without disadvantaging some people.

Maybe one possibility for your wife could be to measure the cleaning equipment and see if it might fit into a smaller car and potentially buy cleaning equipment that is more foldable that might fit. Usually even these small cars have a lot of space when using the back seat row. A big vacuum and mops should easily fit. If this is not possible then I completely understand your problem.

The bigger issue I see with this is that, when your wife would do everything to save gas, she would need to take some disadvantages, e.g., more uncomfortable to load the small vehicle. If there is no pressure for other people, she would be the only one doing it, making it unfair. That’s why it is so important to generate pressure on climate damaging behaviour on all fronts. And this action is one efficient and realistic way to achieve that. But of course you can make the movement more unpopular in the general population… It is really difficult to find and decide for a solution here…