what?

No, she's gonna take a leak

That would seem more likely.

OR she might still be wearing kiyoshis underwear

Maybe she has both?! Now that would be a twist. Σ( ￣□￣||)

Anyway I hope they will get along.

No, she liked having a "connection" to Kiyoshi, which she had when they wore each other's underwear. That's why she demanded that he keep wearing hers.