I guess my issue lies with the thinking that DD needs to be straightforward, because people like AG don't take hints. Except... I'm not sure I see where AG was given any hints. If DD didn't say anything to her at Homecoming when this happened (which I certainly don't blame her for, because that's not exactly easy), then AG probably just thinks they hung out together at Homecoming. (I wouldn't necessarily call the "running away" a hint, because as I recall we were all always sprinting off on one direction or another at dances - when they played a song I liked and I had to dance rightthen, or my best friend saw that boy she liked was finally standing alone, etc.)
I would also bet that AG is following someone's advice. OP says that the two girls never see each other outside of school, but what if AG is saying to someone (mother, therapist, guidance counselor) "DD is so nice in class. I wish we hung out more outside of school." That adult is going to give her advice to get to know DD like: "If you share a class, try to partner up with her"(Spanish) or "If you know you'll both be at an event, hang out with her there" (Homecoming). And if DD is being nice, as it would seem she is, then AG probably thinks she's making progress.
Count me amongst those that feel for both girls, because neither side is fun.