There are a whole host of things between cushings and liver failure. I did look it up and while not as prominent and not all the time there is a smell with cushings.

If i was to make an educated guess on why your vet is leaning to cushings, is with cushings you have arthritic signs and it takes a long time for it to become noticeable whereas liver failure usually sees a rather quick decline.

There are 2 types of cushings (3 if you count the type that is caused by a liver tumor) and frequently there is liver and pancreas involvement that resolves on its own once the cushings is under control.

I wonder if any of her future tests, or past test for that matter, have looked at lyme disease? Long-term lyme disease will eat up a liver.

Two years ago when Sasha was doing really bad, Mary took some x-rays.  When she commented about Cushing causing an enlarged liver / growth on the live I remembered her comment that there was something there but (since we were targeting joints) she couldn't see it with any definition.  We're going back in on Monday at 9:00 (may as well be dark thirty since I have to be on the road by 7:30 at the latest to get there at 9:00) for a more extensive blood work pull.  She gave it a name but my 74 year old brain doesn't remember what it will be.  She'll also do x-rays of the abdominal region this time ...
This is gonna get expensive ....

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It's funny, everything I'm being told is that she's in pain.  It's hard to tell when she goes chasing the kittens.  They walk under her and I swear they do it just to get her to chase them!
Setting / laying down ... that's a different matter, sometimes it's real obvious that she's hurting.  Mary asked about painkillers, my response to her was "As long it's occasional pain, I'd rather not.  Most of the painkillers you talk about warn about live damage and we're already looking at that ... when it becomes a constant then we'll go that way." Okay, I'm hard hearted but ...

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It's odd that her clock is off - it seems to be running fast. Breakfast is after I get up at about 8:00; supper is about 6:00 PM but she's started whining for it about 5:15/5:30; evening treat is 9:00PM and she just started whining for it - at 8:00PM There is almost no difference between her "Daddy, I hurt" and "Daddy, it's food time!" whine, all I can do is go by the clock and / or what she's doing.

I wish you luck on the testing. I know very little about Cushing's in dogs. I am aware of steroid induced cushingnoid signs - I have that, but mostly just thin skin and Buffalo hump. I was not aware of the severe liver enzyme elevations. Hopefully Mary will find something treatable.