It certainly is an interesting topic for many!
I can only explain from my understanding of Karma. Others will have different opinions.
To answer your question, yes, you and your friend are accumulating bad Karma for yourselves by wishing for suffering on others.
If there is any possibility or means of getting justice under the law, your friend can certainly follow that.
Her abusers might or might not get the full punishment they deserve here, but whatever 'debt' of their Karma remains will inevitably have to be repaid one day.
Your or your friend's wishes will not change that one bit.
Everyone enjoys or suffers the consequences of their own good and bad Karma. Others' wishes or actions will not affect those Karma.
Your friend say she believes she was bad in a previous life and seems to accept that her sufferings are a consequence of that.
I would agree with that, but one is usually bad and good, so she would have accumulated good Karma as well.
I hope the sufferings are now behind her and and the consequences of her good Karma will prevail.
Being a 'good' person is a good thing, but it all depends on what is considered 'good' in what society.
The important question to ask is what sort of behaviour and lifestyle creates bad Karma for oneself?
And then to avoid that sort of behaviour and lifestyle.
I won't say anything more on that, but you and your friend can try and find out more about the religions/philosophies that have had Karma and Reincarnation as fundamental concepts for a long time - Hinduism, Buddhism, Sikhism and Jainism.
These are my personal views in response to the question by Windchimesandsong.
Others will have different views and I have no problem with that.