Captain, can you stop her from bein' cheerful, please?
I don't believe there's a power in the 'verse can stop Kaylee from bein' cheerful.
She doesn't claim to know much bout ships, they just...talk to her. Knows Serenity so well she might just be part of the engine herself. But that ain't half of why she's dear to the crew...or to us. She's got a heart you'll see, and can't help but protect like a little sister.