Given how many callback jokes are in this show (like Marco’s hate for wet socks in Game of Flags) I wouldn’t be surprised if it was meant for her to have stolen it using the keys she got from Marco in Mewberty. “Why” did she so that, I don’t know. To mess with him? Because she’s a thief? Dear god plese we don’t need any hint of her having a crush on Marco there’s enough ship suffering as it is
Love tetrahedron with a SafeKidxDelinquent dynamic…
Either she crashed the slumber party and Marco had to give it to her (sounds unlikely, this episode being after Girls’ Day Out it would make sense for Star to want Janna there), or she has stolen it using Marco’s house keys from Mewberty.
Either way this pushes more and more on who the true Jarco duo should be