First, I am so sorry about your dog. I lost a beloved Russian Wolfhound to osteoscarcoma and I never regretted opting for euthanasia as soon as I saw that he was dealing with pain.
So here's the thing. Your snake is in a different situation. Honestly, I either totally missed that previous bloodwork showed inclusion bodies or you didn't mention it. It doesn't matter either way; I just know I didn't pick up on that important piece of information. I get it now why you are reacting strongly to everything - you are dealing with stress and loss.
It's significant that your veterinarian found inclusion bodies previously but even if that diagnosis were to be confirmed (and I understand why you are not re-testing), you SHOULD NOT EUTHANIZE UNLESS THE SNAKE DEVELOPS ACTIVE ILLNESS AND POOR QUALITY OF LIFE. Please know that I am not saying you are considering euthanasia for no reason. I am saying that our current understanding of these viruses tells us that euthanasia should not be considered the first and primary option.
I put that in caps because contrary to earlier beliefs, it is now quite clear that even snakes infected with IBD or Nido may not ever become ill and/or if they become ill it may be relatively mild and still allow them overall excellent quality of life. Someone with a big collection of snakes may opt to euthanize just to reduce the risk of the virus spreading, but in the case of someone with one or two pet snakes, then the main question becomes quality of life.
So for now, just love your snake. I'd personally just not worry about trying to give her probiotics unless you can find a stress-free way of giving them. I'm not seeing any clear indication that she needs them, and while giving them will not cause her any harm, it sounds like trying to get them into her is stressful for both of you and the additional stress is definitely not good for her.
I love that you are working on a jungle gym - just take it very slow and easy with her. Any of us who had spent half of our lives being very inactive would have a tough time with increasing our activity level. When I have taken on snakes who were never offered real opportunities to exercise before, it sometimes took weeks or even months for them to realize that they had more behavioral options available and it definitely took time for them to start exploring these.
Hang in there. I know sometimes we may come on strong with opinions or recommendations, but please know that everyone who has been involved in this thread cares very much about you and your snake.