Most Helpful Girl
After a fight people can become irrational in their thinking. So she probably means she needs time alone to calm down , so she can think more clearly. Then speak again when her thoughts are more rational.
People often say and do things they don't mean during an argument. They make rash decisions and react out of their negative emotions, but when they've calmed down they can communicate without the anger & hurt there. That prevents them saying things they don't mean.