Should my future stepdaughter make a promise during our wedding ceremony?

My partner read his eight-year-old daughter the line he'd written for her: "I promise to love our new family every day." She asked, "Even if I'm cross with you?"

He intended it as a way to include her, not a test. She likes the idea of standing with us but doesn't want to say that sentence. I suggested that the adults make promises to her instead. He worries that removing her part would make the ceremony feel like something happening around her.

Her mother knows she is being included and has asked to see the plan. I want us to send something we're all comfortable with, rather than present a finished script and ask the child to rehearse it.

What would participation look like without asking her to promise a feeling? I don't want her question turned into an adorable line we quote during the ceremony when she was trying to tell us something.