I wish you the best, and I just want to say, I commiserate with the problems re: there not being enough hours in the day, and how it can be difficult getting a dog, and then realizing that your schedule is not as static as you thought it was. When I got my puppy, I was working 9-5 and was sharing an apartment with my girlfriend, who worked similar hours nearby. Well, her company went under, she had to move back to Houston, and while I live 10 minutes from my office, an outside work project I'm involved in has unexpectedly gone into overdrive, leaving me with little uncommitted time, and no one to help me out with the dog.
It kinda sucks, but I guess life can be like that sometimes.
One thing I would say to keep in mind is that your dog needs mental as well as physical exercise. I can pretty much wear my dog out, and he'll still go crazy later, if his day has been restricted to laying in his crate, going on a walk, and then just hanging out in the house. How boring is that, to be locked up pretty much all day long, and just get a half hour of walking, and maybe chase a ball for a bit?
I don't know if you can take your dog to a dog park, what with all of the medical issues you've got going on with her, but I've found that to be a great way to get my guy tuckered out on days when I just don't have it in me to take him on an extended hike. I can take him to the big park downtown, and just sit and chat with other dog owners as he runs around and has a great time. It's a lot of fun, especially for him, but for me as well.
I also teach him tricks. I'll use bits of cheese or freeze dried liver as treats, and train him to do stuff on command, working in short five minute bursts. Maybe while watching a TV show, I'll work on the trick during commercial breaks. I started with sit, down, drop it, and stay, but shake is a good one, if I say "crucio!" he flops on his back, and if I say "loop the loop!" he makes a figure 8 around my legs. That stuff all exercises his brain - he knows I have a treat, he wants it, he has to figure out what to do to get it. He's thinking hard, trying to figure out what this game is, and that's much more of a break from his crate time than trying to figure out how to nab something out of the trash can.
And there are still those days when I'm in meetings at work and can't make it home, and then have obligations in the evening, and I'm torn up knowing that my loving pet has been locked up for most of the day. There's no real solution for that. I just try and make it up for him the best that I can. If I'm tied up on Monday and Tuesday, my dog is going to have an awesome night on Wednesday. And I'm going to steal as much time as I can on Monday and Tuesday to make things bearable for him.