Hi,
I'm so sorry you're going through this.
My first Yorkie turned out to have megaesophagus...sounds like the same thing in a different spot. This was in the 80's and I took her to Angel Memorial, which is a big deal animal hospital, here in Mass.
Anyway, they told me nothing was to be done...she'd starve because the food would stay in her esophagus and never make it to her stomach. That they had kept large dogs alive using a centrifuge, but it wouldn't be practical at home. No kidding? Sheesh.
Prognosis aside, I kept her going for 4 years, despite the naysayers. All I did was feed her, then pick her up...hold her vertically...then gently pound her back. I could feel the big bulge in her throat (where her food was just sitting)...then I'd hear this big kind of glopping sound, and down it would go. If I didn't do this, she'd eventually regurgitate the food. Her esophagus just wouldn't contract and do the job on it's own.
All this rambling on is merely to make the point that maybe you could do a similar thing to encourage her colon? Possibly a firm rotation (in the proper direction...not sure what that is) with your hand, on her lower abdomen? The poop is there...just is not moving along, right?
By the way...megaesophagus is not what killed my Josie. It was a combination of many other organ failures...
Don't lose hope...maybe you can actually deal with this, with a little ingenuity.