All of you were right- getting a stroller was exactly what we needed to do. I've spent the last 8 months walking out a block and back and we're both so bored of that routine.  It's been lovely for taking her to the park and around the city when we're running errands. 

It's also been difficult to find activities to entertain her that don't involve a lot of movement or food. Long rides are perfect. She gets to sniff and see new things, and doesn't get sore. I feel like we've given her back some of the mobility she's lost recently, just in a different form. 

For those of you who might be curious, Jack's just over 30 pounds and we first bought the Pet Gear Jogger, which says it's designed for dogs up to 70 pounds. It was a beautiful stroller but way too small, so we exchanged it for this one, the Expedition (thanks to the positive reviews by others here). It's great-I'd highly recommend it to anyone else looking for a stroller for a medium or large dog.