Not sure if I understand ... but wondering if it might be like the crate covers I've made for my wire dog crates. The crate covers are basically a top piece that fits over the top of the crate and 4 "curtains" that hang on all four sides. On mine, the back and two sides are seamed together but the front curtain is not sewn to the side seams so it can be lifted to allow the dog to get in and out through the door.
Is this what your talking about?
Edited to add ....
I looked up images for isolette covers and I think what you are looking for is similar to the crate covers I used to make. But even better than me explaining .... I found this that might help!!
http://quilttallahassee.com/activiti...olette-covers/