The example she gave in response, involving a boyfriend, yes, would have been someone in her histories. She did previously give a separate example of someone who would not have, though, that being the admirer who stopped by late one night that she let in. If I understood the situation correctly, he wasn't someone in her social circle that she'd been corresponding with previously.
I think the problem you're having with this case is that you keep discounting scenarios due to their likelihood. The issue there is that the "likely" scenarios have been investigated by LE and explored on here exhaustively. They all have a piece that is impossible to make fit. With ETJ, he has an alibi and the DNA doesn't match. With KR, there's the male DNA and the difficulties with incorporating that. The DNA actually is a problem for ANY male in her social circle or that she interacted with that night.
That leads us to have to consider "low probabilities". A random prowler. A distant admirer/stalker. A hired killer. A Craiglist rape ad. A royal screw up in the lab. Considering that what's likely to have happened didn't actually happen, we can't just say a scenario had no chance of happening just because it had a small chance of happening.