Stolen Earrings

"Kaitlyn!" I shrieked when I saw my best friend run through the door, "You're back!"
Kaitlyn had been vacationing at Myrtle Beach for a week and we couldn't wait to see each other. She glanced at my ears. "Where are your earrings?"
She was referring to a pair of earrings she had bought me for my birthday just before she left. They were small, shiny blue crystals dangling from a short silver chain. "I haven't put them on yet; I was planning on wearing them today." I rushed to my room to retrieve the earrings, but when I opened the door to my jewelry box, they were gone!
"I'm positive I put them there before going to bed. I know who must have done it!" I hurried into the living room, where my two brothers and sister sat, lazily watching television.
"Which one of you stole my earrings?" I demanded.
"What would I want with a pair of stinking earrings?" claimed Zack, and Jeremy quickly agreed. "It's not like we wear the things."
"I didn't steal your blue crystal earrings," said Sabrina. "Then who did?" I asked.
Kaitlyn smiled. "I think I know."

Who stole the earrings? And how did Kaitlyn know?