I was told she was a hunter, not a warlock. Could be bs, idk much about her. What I do know is that the hive obviously have a strong influence over her. What leads me to believe that she might betray the city is what she says in the final cutscene, that she understands her role, and will not fail. Oryx is dead, what role is there left to play? Unless she is referring to leading the awoken, which might possibly be true considering we still don't know if Mara's unseen friend is Eris or the guardian, I can see no other possibilities. We have yet to see much about Destiny 2, or Eris' involvement in it, but I firmly believe she is struggling to hold on to sanity, and her loyalty to protecting the city, not to mention despite being a guardian, we really don't know much about what happened to her in the pit, or what became of her ghost.