he, she, it. Whomever called it in. She is just my go to when I'm speaking generally.
Although, I am working under the guarded assumption that her mother called in until I hear otherwise. It very well could be that she called her boyfriend and he called, or that she wasn't even home. Who knows for sure.
ETA- and it's entirely possible that they had a tip off the abandoned house in some way that it was checked first. I agree it's a VERY short span of time for everything to happen, even with the close proximity to the police station. They are super efficient, but even then it's quite something how fast it developed.