When she was young and with Marco she wrote a code/virus designed to disable a reactor so they could board the disabled ship
marco changed the code to blow up the reactor and it killed lots on luna
which is probably why she left Marco in the first place
Marco tried put that same code on the Roci (this season), that’s when she saved Holden when she put together what Filip meant about saving her life
its notable that we saw Cyn leaving the ‘dummy’ ship presumably jerryrigging it - I’m assuming he left some way for her to rewrite the code