Despite declining being an "official" member of these Teen Titans, Kara still wanted to at least make friends and offer to help in case of emergency. Sort of like a reserve member. She was pretty excited to get an invite to their Thanksgiving feast (something she had never been to before). Her and Bart arrived together and apparently just in time to see Spider-Man.
"Woah, cool," Kara replied. Maybe a little too loudly.