Her relationship with Ronaldo at the time was a secret, the only person who knows about this is Kick and possibly Gunther after he joins Kick in delivering a meal to Ronaldo's house in "Stand and Delivery".
In "Snowpocalypse!", Kendall has a light pink cellphone with a different format, but in "Hand in Hand", she appears with a pink normal cellphone.
Kendall's presumed crush on Kick is officialized at the end of "Detained", as it is shown that she had written "I ♥ K.B." on a locker with her favorite pink pen (this is what had gotten her into detention in the first place).
In "Kyle Be Back" it's shown that Kick and Kendall are next-door neighbors but this fact isn't mentioned until "Kick or Treat" when she voices it.
In "Kick or Treat", Kendall's surname: "Perkins" is mentioned as her surname for the first time (however, in "Hand in Hand", she intends to disguise herself as "an heiress; the sole benefactor to the "Perkins" estate" while in the Make-Up shop).
Kendall seems to have her very good habit of farting, due to being gassy. This is hinted in "Stand and Delivery" and later seen in "Hand in Hand". However, she farted on the lamp.
She likes lots of adults in Mellowbrook (except Harold Buttowski (especially in Crumbs) and Ms. Chicarelli).
In "Tattler's Tale" it is shown that Kendall owns a soccer ball which shows that she has some athletic interests (whether she's on a team or just practices with it is unknown since this isn't shown after this episode).
In "Pinch Sitter" Kendall states that she's 2 weeks older than Kick. However, Sandro Corsaro has stated on his Facebook page that Kendall is in fact "two years, three days, fours hours and twenty two minutes" older than Kick. Since Kick's offical birthday is February 22, 2000, this would make Kendall's birthday February 19, 1998 but it could be that this statement isn't meant to be taken seriously as the pinpoint accuracy of Kendall's age in relation to Kick's makes the response sound humorous.