why do you think rosa hubermann always wanted to appear tough and unemotional?

This is a good question. Rosa doesn't show her love openly. She is a bit abrasive and insulting, both to Liesel and Hans. She, however, displays her love in more practical ways. She always makes sure they are fed and taken care of, even in the most dire of circumstances. She protects them and takes care of Max, and other stowaway Jews, who mean so much to Liesel and Hans. The war was hard on people and some show their love in the best way they know how.