She wonders if It can see that she feels guilty. Because Melanie only got caught looking for Sharon, so it's really Sharon's fault that Jamie's lost his sister and that Jared's lost the love of his life.
But Melanie chose to come, so it's not really her fault.
She can't blame herself.
Or at least that's what she tells herself until the thing wearing her cousin's body walks through the caves like she's got the right to be there. She can see the pain on Jamie's face, the agony on Jared's.
And it's her fault. Because of Melanie got caught.
No, it's not her fault. It's not.
It's that thing's.
She hates it (because it's her fault).