Notice that when she refers to Hiccup her facial expressions change too. When Heather says he's cute Astrid gets a dreamy look on her face. And also, Heather's a hard-core Hiccstrid fan; she ships Hiccstrid all the way!
♥Hiccup is my favorite character.♡ I wished there would be an episode where Hiccup gets amnesia and the other Riders have to reteach him about Dragons. Of course, it ends in disaster as Hiccup is the best in the Dragon business.