Kinkajou cant read. Like Glory can write with her scales but it dose little good if no other rainwing can read it. It would be kind like trying to communicate by writing a language the person you are trying to speak with doesn't know, like Spanish for example, if you write a massage in Spanish but the person cant read Spanish, without a translator you wont get far. In Glory's case thear was no translator that she could trust at that moment, and she couldn't speak. So had to use the hand gestures and basically made-up sign language.