When they are that small, and if you are making one for her in the hospital, I would call the ICU and ask them what size would be best for her isolette. They are usually considerably smaller. :D:D:D
OR ask if they would allow you to make an isolette cover. It really makes for a bright spot in her ICU area. They can tell you what size is needed for that also. For my grands, it was a oblong shaped quilt :D:D:D