C.
I have been on several "vacations" to Arizona with my hubby and our 4 kids over the years. The in-laws have a child-proof home and it's still a LOT of work! I have an overactive 4 year old who still finds things to break and destroy in a child-proofed home. My hubby goes and spends time with his family and I get left to deal with the kids. My hubby and I fight constantly when we go and it is sheer torture for me. The last time "vacation" time came around, I found a perfect solution. He took all four kids with him and I stayed home!
Back to your problem... :) I do think it is inappropriate to expect another woman to adjust her house for 1 week of the year. In a perfect world, she would do it on her own (the grandmother), but if she doesn't, then I think you should just take lots of walks. Stay out of the house as much as possible. Go to a hotel if that is an option. They have extended stay places that are cheaper if you stay a week or more.
Best of luck, though. I know it is a hard situation to be in!