First Amendment
As police officer reporting assault by another officer was neither acting as a private citizen nor speaking on a matter of public concern, her subsequent demotion doesn't violate the First Amendment.
http://media.ca7.uscourts.gov/cgi-bin/rssExec.pl?Submit=Display&Path=Y2016/D01-11/C:14-3074:J:Flaum:aut:T:fnOp:N:1685011:S:0
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.