You asked what would I do...boy...
Decide if dog's problem is neurological first. Why? Because if it gets worse she will lose bladder control.
Get imaging of the spine if I can afford it. Get physical exam from regular vet if I cannot. (Vet will do simple office tests to check feeling/reflexes in hind feet. A physical exam should give a yes/no on whether it's neurological at this point, as prounounced as her symptoms are.)
If imaging or physical exam shows it is not neurological, proceed to get cart.
If physical exam indicates it is neurological, stop everything and put dog on crate rest for a month or more, probably with prednisone. This assumes I cannot afford imaging like an expensive MRI/CT/myelogram and have no way to know if the neurological problem is a disk or a tumor or something else. Dog may or may not improve with rest if it is a disk. Dog probably will not improve if it is a tumor. If the dog does not improve with rest, decide whether I will be able to provide bladder care if she loses bladder control in the future. If yes, proceed to get cart.
I would get her a quad cart, I think I have pretty much decided against a 2-wheel cart where you attach extra front wheels. Bobbie or Nancy may have a clearer idea of this, I am stretching to imagine it. When you put her hindquarters in the 2-wheel cart, the dog normally stands on the 2 front legs and the hindquarters are lifted. With an Eddie's cart, the hind feet are lifted several inches off the ground and put through the leg holes. With a Doggon' or Walkin' Wheels, a harness is put on the hindquarters and the hindquarters are lifted to a standing position (not off the ground) and the harness is fastened to the cart frame. But even if you are not lifting the hind feet off the ground, it is still going to be a stress on the dog trying to support herself on one front leg while you are putting her in the cart, because her weak or limp hind legs are not going to stabilize her front end like they used to do, and your manipulations of her will have her off balance while you clip the harness to one side of the frame, then the other. Her ankle will be wobbling left and right, her knee will be swaying left and right, her shoulder and neck muscles will be straining for balance. She may mess up her ankle, knee, shoulder or neck if you do this 2-3 times a day every day. Then she's in pain and you have a real mobility problem with that last front leg compromised by a "sports injury". A work-around for this problem is if you could have a partner steady her in front so she can be put in the 2-wheel cart safely without hurting herself in the process, then you attach the extra wheels.
I have only tried 2 quad carts, and I liked Doggon’, I would buy it again. I have not tried the K-9 cart, it looks very maneuverable, too. I would measure my doorway and ask them how wide their 4-wheel cart would be for a dog this size to be sure I can get her out the door.
And finally, I would have to use a mechanical lift to get the dog into the cart, that’s what I had to do with my dog because I couldn’t lift him. It was not expensive and I have instructions how to set this up if you need it. I certainly wish you the best whatever you decide.http://www.handicappedpets.com/mediawik ... _heavy_dog