[souffle]

It's hard to tell really - sometimes they go up and down and have good spells then drop down again. When they stop eating that is usually a sign that the may be approaching their time. As long as you don't feel she is ill or in pain and is still pottering along I would spoil her and make her set up easy and comfortable for her. Put in maybe a water bowl and easy reach food as well as a little soft food like babyfood or porridge. There sometimes give a little boost.
right before they leave us they become unable to control their temperature and will feel cold. They often leave the nest and lie out as their body prepares to cross the bridge. The last breaths are deep and often quite far apart.
I hope her twilight times are comfortable.