There is a sentence what I hear too often "cancer for it different forms is very common, so there is almost no family what haven't lost a loved one to this illness". But it usually been told about humans. Although this sentence is true for your "animal" relatives as well.
She is still happy, eats well and even chases cats during every evening walk, but it's being more and more difficult for her with only three properly working legs.
We can't know how long she will live, it's a matter of months. I hope that I will be able to get home at time before she will go to her final sleep.
Meanwhile we'll enjoy the regular walks and be happy when she is happy!
I was supposed to work more on my "Foxes of the Seasons" project, I am not sure what I will be able to concentrate on it right now.