A bit more about Chris Kyle. He and Missy both were fitness trainers so it wouldn't be surprising if they knew each other or had some other professional link(s). I searched the thread archives and there really hasn't been any discussion of Kyle apart from this description of a local comparing the community responses shortly after each homicide. I don't have a theory on what relevance this might have apart from the ARG/geocache gone wrong hypothesis.
TX - Terri 'Missy' Bevers,45, murdered in church/person in SWAT gear,18 Apr 2016 #16
People bump into people. So Missy and Kyle could have "crossed paths" or even met at some point, although Midlothian is part of a massively-populated world (the DFW area) rather than a small, isolated community where people who live there would necessarily have ties to everyone else.
But re the fitness angle, I don't know exact timeline specifics of her life history, but my sense is that Missy was not likely to have crossed paths with Kyle in the fitness biz because their "when" and "who" were so different. Kyle's death was more than 3 years earlier than hers. It also seems like his business was a selective world/clientele of military and ex-military people, while hers was suburban families and soccer moms.
In any event, there's nothing similar about their deaths at all, other than they were both murdered.