On one hand you are right that it does seem like psycho behavior but the counterpoint to that is Ella has been completely loyal to her two friends which they are reciprocating. It's not psychopathy in the sense she doesn't feel empathy but that she prioritizes love of a friend above all else. There is a big difference between a lack of empathy and absolute loyalty despite the other parties flaws.
Imagine for a minute it was a relationship between a husband and wife where the husband was a mercenary but at the same time was a loving husband and father. From the wife's perspective her man has always done right by her and the people he kills are no friends of hers, should she throw away a long relationship with someone who loves her unconditionally just because he does bad things to other people? From a purely moral perspective, yes, but life is never that clean cut.
How many women have been loyal to husbands who were soldiers in a militaristic empire? Are they all psychopath's?
Also, she's a stripper with loose morals who works in a strip-joint owned by the mob, what do you expect?