...damnit. I was this close to getting PROPS. I didn't have time to check the idea before I left for work, so thanks to the guys that did. I watched the two different clips just a few minutes ago. Yeah, Alex's "girlfriend" was blonde with chipmunk cheeks. Jessica is brunette and has a longer face.
Either way I'll be interested to see if Alex's girlfriend shows up, seeing as how Alex was doing the whole "you run I'll be right behind you" thing.
I'm going to type while I work an idea out here...
So all of Jay's memory loss episodes all seem to involve actual contact with totheark, where as everyone seems to get sick around Slender Man. So...
1. Has anyone considered whether or not "totheark" is actually Alex, Brian, or Tim? All of them have gone missing. Alex's "help me" video is directed at Jay using the same medium that totheark is posting videos. All four characters have dark hair, but Jay has been seen in screen with totheark at the same time, so what if totheark is someone that's been taken that's trying to communicate with Jay? The wiki for MH says that totheark is almost certainly Tim, which seems to be a conclusion drawn from the hairstyle and the jacket type worn by Tim in other clips.
Now Alex has officially gone from missing to something worse, so perhaps Alex is going through the same process that totheark went through? the totheark entries on the wiki are pretty interesting to read.
My money is on Jessica being somehow connected to one of the actors involved in Marble Hornets, and that she recognized Jay perhaps from pictures or video she received from someone now missing that's become involved.