What you do is say you are coming and wait for the response. Judge you decision by what is said. You might get a big thank you or a lukewarm response. The lukewarm response might make you decide to just stay a few days until she is back up on her feet.
I was going to stay with daughter for a day or two, but could not put up with the dogs and other things. So we came home after one day. But, we did not have to go so far, just a two hour drive by car.