Deltarune - Suselle Time

Suselle time?
Nah, sorry pal, not interest… For me there is only one type of time… PIZZA TIME

If Noelle does join the party I see it happening one of two ways.

The way depicted here. Or, she catches Kris and Susie sneaking into the closet, smiles on their faces. She freaks out and chases after them, thus falling down the metaphorical rabbit hole.

Either way it's due to a high-larious misunderstanding.