What to do with negative research outcomes (results) of PhD research experiment?
Your friend might not want to hear this, but there's nothing you can do except for start over - with a different experiment. Research fails - and should  ! If there isn't a risk of failure, you're not out on the cutting edge doing research. 

But in most failures, there's a grain of something to build on ("from the ashes of disaster come the roses of success"). Maybe the student is too demoralized right now to see it, but almost always there's some clue in the failure that leads to a different research question worth asking.