Jet and Sam clearly have the advantage here with regard to persuasive ability. They're the ones who know Bucky after all, and she can't honestly blame him for not wanting to wedge himself into a sandwich with a stranger in his midst. But Terezi also has persistence on her side. Sam might know how to take no for an answer, but she doesn't.

"Is it me? It's me, isn't it? Look, I will just scoot my bony self over this way and you won't even know that I'm here." In the middle of the hug sandwich, Terezi wiggles and worms her way to the outside of the group hug so that she can use Sam and Jet to obscure herself from view. "There. You can't see me, I can't see any of you. We're golden. Come get your manly friend-hug on."