For children paying attention, with highly tuned senses but little background understanding of how grownups view the world today, just about everything is miraculous--singular events that rock their worlds.
Post-Newtonian physics has closets full of ghosts, spirits in impossible worlds conjured by mathematics. If a 3rd grader spouts off a question a physicist may reasonably ask ("Ms. Santanella, can today happen again?"), that child's question will be dismissed with a cursory "Of course not!"
So what do you say? You can offer alternate explanations that fit the data and a larger worldview (which is what scientists, do, no?). You could ask her to continue her observations. You might even help her set up a way to test her hypothesis that her ghost exists.
What you shouldn't do, though, is just dismiss it. Even if the bell is about to ring and the state-mandated testing is 3 weeks away.
My 1960's public schooling tried to squeeze a mechanistic view of the universe into my skull--I was stubborn enough to know I saw enough at the edge of a pond to dismiss what passed for science in school.
I didn't know enough to challenge my teachers, but I knew enough to know they didn't quite have the whole story.
We never have; we never will. That's what makes science so much fun....
Multiverse drawing from Nature, 443