I could be wrong but I think the Sheriff determined that Jayme was home "because of the 911 call and evidence at the scene" (paraphrase mine) before any attempts at enhancement of the call. We can't even be sure when, with everything happening in those first hours, anyone in LE was able to listen to the 911 call, enhanced or otherwise. This suggests to me that it wasn't what was ON the call, but the call itself, that leaned them to believing she was there. MOO, I think they assumed Jayme had made the call, because her parents, at first blush, couldn't have. As for evidence at the scene placing her there, I would guess that could be as simple as a slept in bed and no evidence that she had been elsewhere. Logic would say, barring other information, a 13 year old would indeed be home, in bed, and likely asleep at 1 am .... perhaps it's no more complicated than that.
JMO