Glad she is feeling better! If you need to fatten her up, you could give her some chick starter, it has higher protein than layer. Just make sure she has access to calcium if you do. I've had a couple of girls get slightly impacted crops, but a good massage and yogurt usually does the trick.
I may just pick up a small bag of chick starter. She had diarrhea for about 1-2 weeks and I think she lost a lot of weight from that. My grandma got the full fat plain Greek yogurt so that has plenty of calories, so maybe that will help to. 
