Translation:I need to settle the score with her.
"Settle the score" (I dont think it's ever plural in the idiom) comes from the mid-1800's when score meant "account" or "bill", so in some ways is literally the same as the Portuguese expression (from the origin), except now most people use score to mean something like the amount of points in sports, so that usually comes to mind when this is said. It means to make things right between people (end a conflict or an uneven situation) and can mean by using revenge or simply talking. It basically hints that the person is getting what they are owed, so usually is used in a negative way such as revenge or avenging wrongs against someone.
This is a very common expression where I'm from.
That has a positive connotation, usually. To get right with someone, to make things right with someone, or to make up with someone - these are all related. They imply talking or taking action to repair a relationship or just to balance out a wrong that was done to someone else.
To settle the score is more antagonistic, at least in modern use. It's also used as a noun in the form "a score to settle". Both usually mean some form of confrontation will be involved, possibly even revenge.
So I guess I'd like to know if the Portuguese phrase has a positive, negative, or neutral tone before I'd use it.
"Acertar as contas" does translate accurately as "to settle the score" --- it also suggests confrontation.
It can also be used in the sense of having to discuss something contentious, similar to " I have a bone to pick with her."
What does this thing really mean. Does it mean that the speaker just wants to 'pick a bone' with the one referred to or to do something to get back at them for something they have done in the past? Settling scores in my experience never means simply scolding or shouting at someone.