Aggressive female ecletus

[Tburns]

I adopted nalanis when she was 5 yrs old I was told that she had been rehomed 5 times before I adopted her because she was aggressive and would attack people . I've had her now for about 3 yrs and I have spent a lot of time helping her unlearn some of her aggressive habits but she still for no reason out if the blue will try to attack me it does not happen alot but when it does she scares me and her bites are really bad very bloody and I try to be calm I don't yell at her I just firmly tell her no biting out her back in her cage and ignore her is this the proper way to deal with this behavior I don't want to make it worse but it's hard for me to trust her when she wants to be on my shoulder