Don't really know but can only theorize (if it's connected). From what I've read, I think the investigation has been underway, and continues to be underway. One deputy was arrested right before her murder, one after. Can't really know if Missy had anything to do with those arrests, but since Texas Rangers are still investigating the ECSO cases, there could conceivably be more arrests coming.
My own theory is that Missy knew something, but that 'something' was likely more peripheral than direct - and maybe she was killed for the investigative chain reaction it would set off, not so much for the seriousness of that one tidbit of information.
For example, what if she were wrestling with knowledge of illegal drug sales at the gym, or perhaps was concerned about discovering illegal drug use by someone she knew...and maybe she had personal reasons for not initially reporting it, but then had decided to override those? Following that hypothetical scenario, say she were to decide to report that discovery...and the investigation grew from that one user to his suppliers and the people that worked for or protected them? What repercussions might there be for area businesses, churches, or schools in Missy's circles (depending on where the abuse occurred and where the investigation led)? How many people and families and careers might end up being affected if that one discovery she made dominoes into a larger a web of crime that covers a whole county?