If she did in fact vanish on her run, I think that makes the most sense. The Snapchat doesn't bother me in this theory. Like others have stated, no one ever said it was in fact a "good night" snap. She could have sent it around 730, texted with her mom about dinner, then headed out for her run. Additionally, even if you want to think of it as a good night snap, some people who get up super early for work head to bed really early. Perhaps her bf had made it a habit in the past to turn in by 830 or 9 so she knew he wouldn't be up after she got back from her run and dinner at her mom's.
I agree with the timeline posted above that she got dropped off, tended to the dogs, did HW, snapped, texted her mom, and then left around 730. This jives with what that neighbor said he saw. Now he said she was walking, but she may have been warming up before starting her run full out at that time. Her intention was to run, end up at Mom's, eat, then take the car home, but she never made it to her mom's house.
I do think from LE has said about having FitBit data and her not making it home that they have a pretty darn good idea about where the run stopped/where she was taken or something happened. And I think they may have an idea of a suspect and are watching that person, hence the lack of info to the public.