Anna is ten and a half and puts the younger ones to shame in the zoomie department and overall running full out like her tail is on fire. But, I have noticed that she has been getting up from a nap/sleep more slowly these days and it takes her a minute or so to "get going". In the back of my mind, I am preparing myself for the day that she hits the wall - just stops running with enthusiasm, or maybe not at all.
Maybe is you "rest" Elsie with leash walks only for a month or so (with treats if she's food motivated?), whatever is ailing her might calm down. That coupled with the move to a house without stairs just might be the ticket for her. If it's age related, she may just be self-regulating her activities to cope with her aches and pains. Supplementation might do her some good, too. As time goes on, I am becoming more and more of a fan of Springtime's Longevity. I am not and have never been a fan or believer in the exaggerated claims of supplements for humans or our pets, but I have done my own little "experimenting" with Longevity and have proven in my mind that it has made a difference. Nothing is going to stop the changes that we see in our pets, but I just want to make the decline as slow and gradual as I can.