Mine can do 9 hours. I hate it, but they can do it.
I come home for lunch daily, but if I go away hubby is alone with them and can't do a trip home for lunch. When my father had bypass surgery, they had to do it for a month and were just fine.
Most days, they don't bother getting up when I come home at noon, especially during the winter. When it's nice out, Brees mostly wants to go out to chase squirrels. Lunchtime is more for me than for them.
Sounds like the coat might be the trigger with the walker. Leave a light coat on her during the day and try again?