My 14 year-old border Collie has had Cushings for about 3 years. Because of her age we chose not to treat the Cushings. Over the past 6 weeks she has lost a lot of weight, her legs are giving out on her, shes not eating much, and now she is throwing up a mix of bile and food every time she eats. She is also having diarrhea every other day. She is still in good spirits and not in pain. I'm wondering how much time we have left with her so I can prepare my 7 year old son. Is this days? Weeks? A month?
If she is vomiting every time she eats, then that, although not necessarily *pain* as such, she certainly can't go on like that. She is being very stoical, or brave as dogs typically are. Though it's obvious she must feel pretty bad to vomit each time she eats.
Although you have opted not to treat the Cushing's, you could ask your vet about any possible palliative treatments available to her? (anti-nausea drugs, anti-diarrheals, etc) to make the remainder of her time a bit easier.
And I would involve your son in "Rainbow-Bridge" talks, because there is no time like the present.