I'd say yes, it's a great idea to use cat nappies in your situation. It is because, sadly, given the circumstances, your cat's condition isn't expected to improve since the stroke-related disability is generally permanent and she most probably wouldn't stop urinating and defecating outside of the litterbox. Also you, as the owner, would have a peace of mind since you wouldn't have to constantly worry she is going to contaminate something while wandering around your house.
Of course the perfect solution does not exist and nappies also have their drawbacks. For example it might be hard to get your cat used to them and comfortably wear them, but it would depend on your princess' personality and therefore it's difficult to predict how exactly would it turn out. It would also mean somewhat increased costs, especially if you use one-time disposable nappies. On the other hand, reusable diapers tend to be messy and more tedious. But I think it's totally worth it, because cleaning contaminated surfaces might turn out to be tedious and maybe even more expensive, in case you for example owned something like a valuable, fancy carpet in your house and it got ruined.
So, in conclusion, please be prepared for the possibility that your cat might find the nappies uncomfortable at first, but otherwise it is a great solution. Also, please remember to always remove the diaper as soon as possible if it gets urinated or soiled and to clean your cat after it happens. For cleaning you could use hypoallergenic baby tissues; just make sure they're fragrance and alcohol free. Please also stay vigilant and look out for any signs of your cat's skin irritation, like a rash.