The reason to keep the joey with the parents until she's twelve weeks old is that they will teach her about being a glider. She'll learn important communication and social skills. Also, she'll be more self-confident and not so frightened when she comes to live with you. Ten weeks is certainly better than eight.
I wouldn't try introducing them until she's bigger, probably around the end of summer as Goldwinger said. She simply has to have some size and weight in order to defend herself. It may not be necessary for her to do so, but if it is and she's not big enough the result could be tragic.
Also, if you have supervised visits between them during the time that she's growing and they do get along well, it's not good to separate them and then allow them to see each other once in a while. That could easily stress out both gliders and lead to even more problems.
Anyway, you have plenty of time to make her cage and get ready for her. Good luck, please keep us updated and when the time is right, remember ... we're gonna want pics!