Hey, let's join a morbid cult we know nothing about!

Well it did get better with each passing episode.
It seems to me that she was aware or suspicious of this group but went ahead with it anyway.
Also there was that moment where she witnessed the deaths of two members within the same day.
The girl who snuck into the operating room/table and passed herself off as a cadaver for dissection.
She grabbed Rosa's hand holding the scalpel and used it to stab herself with.
Then later on the man who who had become president hangs himself on the upper level.
By then that would have been enough to make anyone else (me included) to get away from that group.
Later on she kills her best friend Jacob to pass her initiation test to become the next president of this cultish
group.
My impression is that Rosa has a sense of ruthlessness about her and would have been willing to do anything to reach the top and become a successful member of this order.
She felt the need to prove herself, as she was not of the same wealthy class as the rest of the Ares members were.
Also the fact that she is part black may have had something also to do with it.
Maybe she needed to prove to them that she could be as good as the rest of them and just as cold blooded as they are.
Even her friend Carmen backed down and failed to be the president, because she couldn't bring herself to kill someone in order to become the head of the group.