It's such a relief to hear that Sadie seems to be responding well to the treatment. You know, if something like this had to happen, the timing isn't all that bad. While it's not exactly how you expected to be spending your vacation time with Sadie, it's a blessing that you can be with her 24x7 during a crucial time in her recovery.
I'm like Chelle, and just have to wonder if that altercation with the GD a few days ago didn't cause an injury that created the clot resulting in the spinal stroke. It's the kind of thing that could take a few days to develop and BAM! your dog goes down for what seems like no reason at all.
Phebe and I are sending you sweet Sheltie thoughts and hugs and praying that Sadie's recovery will go well and you will have many more happy years together.