There are some specific steps (knock her out before the hobgoblin boss, else she does not remain temporary hostile, and after you knock her out, you need to kill the other two bosses before the long rest, else she wake up and you need to knock her out again), but it’s feasible. There are a lot of YouTube video about it. She is in all my runs (she is one of the funniest companion), and I never killed the tielflings