What she's presently doing is clinging, very stubbornly at that. How she's not cutting herself presumably has to do with the fact that Potato, at the core, has the approximate resistance and stability of a particularly durable water balloon.

Which is to say, she is temporarily an extremely effective, if talkative sheath.

Puffing her cheeks, Potato stubbornly shakes her head. "No way!!! If I move, you'll, um... You're going to try hitting him right??" She points back at Tidus. "And he's from the Train! Which means he's a friend!" She decided it!

More importantly- "And that means, I'm gonna help keep them safe!"