The brain is still developing until 25 (possibly later), particularly the parts associated with empathy.
Your DD clearly has cognitive empathy, she can perceive and understand other people's feelings. When she says she doesn't care, I wonder if she means that she doesn't have a strong emotional response? Emotional empathy can involve strong emotions, like crying, feeling distressed because of another person's plight. Compassion is not such a strong, recognisable, emotional feeling though IYSWIM?
When she says she doesn't care, does she mean if her friend were crying, she wouldn't feel sad or angry about whatever her friend is crying about but she would want to make her feel happy, help her? That is still empathy, that is "caring". Or does she mean she really isn't bothered how her friend feels and would rather to leave her to it, would be annoyed if helping her friend inconvenienced her but only goes through the motions of being kind for selfish reasons because it would be detrimental to your DD not to do it (eg her friends would judge her)? That would be "not caring".
Like many PPs, I didn't have strong emotional empathetic feelings until I was in my mid twenties and had my first DC. I was kind and compassionate though.
How would she feel if she saw someone repeatedly kicking a cat? Anger? Would she want to stop them? That is empathy.