My cat growls at my friend's cats who are visiting but she doesn't get mad when she smells their scent?

I am trying to introduce my cat to her siblings who she hasn't seen a in a while. My friend adopted them and they are staying with me for a few days. The first day my cat growled at everything, even their scent but now she's ok with the scent but if she sees them she gets mad. What does this mean?