C. She hates Aunt Sally's vase.
The narrator says that the vase "actually looked better in a hundred pieces." She also does not take any care when she is dusting the vase since she is leaning over the stairs will dusting it. These details show that she hates the vase. The vase was not extremely dusty because she only needed to "dust it off a little." Also, there is no indication that Aunt Sally wanted her to break the vase. We don't know anything about Aunt Sally's feelings towards the vase or even anything about Aunt Sally. We also don't know for sure that she didn't mean to drop the vase. She uses words like "I swear" to convince us of her innocence but they actually make the reader more suspicious.
