I love her and every thing about her but...?

Okay so I get very well along with my gf and we never fight and i wouldn't change one think about her... but the problem is its very hard to communicate with her when she is upset about something because right away she shuts down and doesn't voice her o pion i handle it in a mature way and i handle it like my parents who are both physiologist taught me to handle relationships but its seems as if she still shuts down and i dont know how to get her to stop being mad at me i try and leave her, space when shes upset but that doesn't seem to work ether... does any one have any ideas of how to deal with this kind of situation she also always says i will talk to you tomorrow trying to escape the situation completely... sorry for the long story but thanks alot for your help!