I read an interesting article a few years back on mega esophagus, and while this case was in a dog, I don't see why the feeding technique they talked about wouldn't work in a cat. When they fed the dog, they fed her so that she was standing on her hind legs, which straightened out the esophagus to the point where the food wouldn't get trapped in the pouchy part. I think with enough work and training, a cat can also be trained to standn like that for feeding, and if so, it might help with feedings.
Ghilly
Exactly what I was going to say...
Depending on her parentage, 1.3 lb. may not be that tiny--does she look emaciated?
Yes. You'll have to be careful with her diet. You'll have to likely avoid the hard foods, and possibly keep her on a mostly liquid diet because of the megaesophagus issue.
There's a megacolon support thread on this forum; here's the link so you can see some of the other experiences of those with cats that have mega colon.
http://www.medhelp.org/posts/show/270440