When hand raising Rocky, rejected at 2 weeks oop, he was about half the size of his sibling until about 10 weeks. He is now 6 and a half months old and the same size as his sibling. I don't know why he was rejected and will never know. There are several stories on this site about rejected Joeys. Some with happy ending and some with sad endings. You might want to do a search to read the stories. Also this sight has great information,
http://www.suzsugargliders.com/helpforrejectedjoeys.htm
Just keep an eye on her weight and start keeping track of it, making sure that she is gaining weight. I used a kitchen scale in grams. In the beginning he would gain about a gram every other day, some times every 3rd day. Please know that I am not a vet and am just sharing my own experience. Rocky did see a vet the day after I started hand raising him and was given sub-q fluids, because he was dehydrated, for the first 4 days. I hope this helps.