It is no surprise that Bri's first real laugh was with her Nana. To this day, Nana is her favorite. And, until this day at Nana's, we had never heard her laugh before.
It's worth noting that this is not the case with Poppy. Brianna has rebuffed her grandfather for 15 months now. She will not go to him, she will not receive his advances, and even at the remote chance that he might make an approach, she begins to chant "No. No. No." We'd feel sorry for Poppy, if it weren't so funny.