So, you have answered your own question.
She is a nightmare and you are nice. Really?
Do what you want. Personally, I think that no matter who we are, we all have faults, that is what makes us human. Some are harder to live with than others, but we all have them.
I have to listen to the same three sentences being repeated ad nauseum when I have my mum, with altzeimers staying. I honestly feel like screaming at times, but I don't, I suck it up because one day that could be me.
My mil is practically deaf, so we need to shout, have the tv blaring and put up with her highly opinionated views. I suck it up because she is lovely, just flawed, like me.
It is a two hour drive north to pick up my parents and an hour and a half south to collect in laws. We do it without a thought (we do have a winge about it though, in private), because they could not cope with public transport, assuming it was available.
But you have obviously already decided not to have her stay and we're looking here for support in that.