Question

get some ice cream instead?
laynas face brightened. \lets go.\
as we, ate, layna told me all about some trick called an ollie. then justin leaned over and sat near us.
\that could have ended badly,\ she said. \you were right.\
\thanks,\ i said, surprised.
\thats what i came to say. thanks. for speaking up like that.\
justin was looking at me in a way she never had before. then she started talking about bungee jumping.
i smiled, basking in the realization that justine, boldest of them all, actually thought i was brave.
why do grandmas words about bravery most likely pop into tianas head?
tiana thinks layna is brave for doing the trick with justine.
tiana knows she has to be brave to stand up to justine.
tiana suddenly realizes her grandmother was wrong.
tiana admires justine and her friends for the brave tricks they do.

Explanation:

From the text, Tiana spoke up to prevent a bad outcome, and Justine thanked her for this act, making Tiana realize Justine saw her as brave. The context implies Tiana needed bravery to stand up to Justine, which connects to her grandma's words about bravery.

Answer:

Tiana knows she has to be brave to stand up to Justine.