If Dawn were to make a cameo in Kalos and Serena blushes toAsh like inXY7, what it wll be the reaction of Dawn to this?
While the likelihood of this is very slim, it's a good question none the less.
Kinda hard to say really, but I guess we can look to the episode where the group got trapped in the warehouse. Lyra began questioning Dawn about her relationship with Ash which got Dawn all flustered. While she didn't get jealous of Lyra claiming that she'd make Ash her(Lyra, just cause this sounds confusing) husband, I do remember Dawn questioning it a bit. Outside of that though, as much as we all want it be, Dawn never showed any signs of jealousy. It could just be that Ash never showed any sort of major concern for anyone else but Dawn during the DP series, so the hints of Dawn's feelings when around other girls that talked about Ash were at a minimum. Instead it was characters around Ash and Dawn that made reaction, none bigger then Kenny though.
That being said, I just might have to believe Dawn might get a bit jealous of Ash and Serena's relationship.