Oh -- I guess maybe I misunderstood the overall concerns of your previous posts -- is the issue really primarily that she is slipping on the floors? If the basic issue is difficulty in walking on floors at the moment, then I'd put down some inexpensive area rugs and runners -- you can get them at IKEA and hardware stores very cheaply. I think those would be a lot more effective than boots (and just be aware than some dogs can find items like boots uncomfortable and more distressing than whatever difficulty they have with slippery surfaces).
Boots also won't do anything for weakness -- ie if she only demonstrates the instability at home on certain floors that is one thing, but if the problem is general, regardless of where she is, then boots are not going to do much of anything especially if the socks didn't make a significant improvement. But I had thought you already had taken steps to get rid of the exposed floor surfaces in the past as she has ben having slipping problems from posts going a ways back I think? and I seem to remember this being discussed then. If some rooms are still too difficult though, I'd close the doors and limit her access to the slippery rooms.
I think you should talk to the neuro about pain however -- it is unlikely any dog with SM, especially severe SM, would be having no or little pain. It is very easy for owners to not think their dog is in pain, as they cover it very well. There are also levels of distress from disability that mean avery poor quality of life for a pet -- for example cats are very disturbed by incontinence. Dr Marino has done a study where they filmed dogs -- they inevitably perked up and wagged tails to see owners but the same dogs were clearly in pain and distress when owners were not there. He made this point at an SM symposium in the Uk to underline that assessment of pain is difficult especially for owners as dogs will try so hard to be outgoing and normal when owners interact with them. Tail wagging cannot really be used to assess the happiness of cavaliers -- they are bred to tail-wag constantly (as can be seen when they are in the show ring) and perhaps this is the result of the fact that they seem to have high levels of the feel-good hormone seratonin. Therefore they likely will often wag regardless of how they feel or hurt, unlike most other breeds. If a cavalier cannot wag that indicates serious distress, but the fact that a cavalier is still wagging its tail really cannot be used to judge pain or happiness.
If I had a dog with generally good quality of life with weak hindquarters as the main problem, I'd get one of those dog carts (assuming forelegs are strong enough for the dog to move about). But maybe it is all four limbs?
I think for us to 'know' it is the right time means really understanding what they are going through and being honest in our own attempts at assessment. I think like Nicki, that most people probably do not know when it is 'time' and probably leave it too late, as Margaret says has happened with her -- we tend to hope for sudden recoveries and fail to see that they are struggling early enough. Experience helps but most of us lack that. I think it is judging the right time before there's significant distress, especially with dogs that have a very limited timeline.
But none of us can make this assessment or advise any more than making fairly general comments to try and be helpful. It is impossible really as we cannot see her and we don't see her daily as you do.
When I lost Lucy to MVD I knew we were in her final weeks but in the end she passed away in her sleep quietly. I would not have tried to keep her going for the sake of a few extra days or weeks had she been in distress and struggling, but she was still very gung-ho and mobile and interested in food and life. Watching and waiting is very hard. :flwr: