This is my first time posting so hope I am within bounds providing my "2 cents".
I think the person who sent her the disturbing message to MB a few days prior (presumably while she was in Austin?) is the same person who killed her. I think this person had a great deal of rage which may have accompanied feelings of needing to be in control (because deep down you feel like you can't control what's happening that is causing the rage) and maybe sending a threatening/disturbing message gave the perp a sense of immediate gratification and a feeling of temporary control to "hold them over" until they would commit the murder when MB returned from Austin.
No matter who it was - no one would never want to have association with the electronic footprint of a "creepy and strange" LinkedIn message to someone who ends up brutally murdered two days later. Fluke? Coincidence? IDK. But I do not think anyone involved in the murder (whether 1 or many) would want MB with her guard up. About the only thing I can imagine is setting up not only a burlgary scenario but also a stranger stalking scenario - and this part seems lame, not enough "creepy" messages.