Is my girlfriend a player?

Inside a handwritten letter she wrote for me and gave me on our relationship anniversary she wrote how she loves me, how she wants me to believe that she loves me, how she fears losing me, how she's too shy to express herself, etc.

But her attitudes speak the opposite of this. I mean, she's loving and caring when she's with me, okay. But every once in while she has to work on weekends and she nevers calls me. Like last saturday she was supposed to call me when she was free from work, but she never called me.
She also doesn't seem to fear losing me. Quite the opposite, she seems very sure of herself.
She doesn't seem to care if my day was good. She never asks anything about my personal life.
She says she wants to marry me, but she doesn't do anything to make the relationship grow more mature.

She also focuses too much on her career and puts that before anything, even before our relationship.

I'm her first boyfriend and she's a virgin. We're christians and plan on having sex after marriage (if that changes anything).

Any help is appretiated.

Nothing you said in this post makes her a player, it only makes her very self involved. She cares more about herself and her life over you and yours, that might be because she is young, I don't know.