Can anyone recommend pet ambulance services in the Chicago area?

My dog was recently diagnosed with bone cancer and its not good. She has a life expectancy of 4 months, maybe a little longer if she is lucky. I have a St.Bernard and she weighs a lot, around 140 lbs. What scares me more than anything is that as the cancer progresses my dog is going to have a very hard time walking and I need to make transportation and emergency arrangements. Because she is such a large dog I won't be able to carry her myself if I have to take her to the vet if she can't walk. I'm looking into pet ambulance services just in case but I'm not sure if there are any other options available.

I have no idea what I am going to do in the meantime as far as her climbing up and down the porch stairs to get in and out of my house. Right now she can walk just fine but probably within the next month or two that may not be the case. I just dread it all.