Why would my girlfriend not want me to worry?

Well my girlfriend was raped a few years ago (before I met her) but what she didn't tell me was that her rapist cut her and left her to die. I found out (not from her) and then confronted her (not angrily, in a caring way) and she said she didn't want me to worry about her. Why would she not want me to worry? It's a sign that I care about her, so why would it bother her?