Personality clashed between me and my GF

I have been in a relationship with a girl that I work with for the last 6 months .... she is 2 yrs elder than me ... she is 27 ..... we were going around well for nearly 5 months .... but since the last 1 month things are not going well between us ... we fight over petty issues and none of us is willing to understand what orther has to say and we argue on everything and end up fighting with each other .... I am a simple guy with good source of earning and a very positive outlook towards life ... however she is too much into her sports and does not want to be serious ... she loves her individuality and do not want any comropmise with what she wants in her life .... although she has been playing this sport for nearly 5 years now yet she has not achived anything from it ... I do not think that she has a future in this sport .... and the time that she should spend with me and planning about our future is being wasted in this sport ... I genuienly want to marry her and we both have spoken about this already ... and the feeling is mutual ... however due to the increasing clases I have seriously thought about reconsidering my decision ... The problem is .. she wants to live her life the way she has been living ... and I am used ot a different lifestyle .... and I alsoprovide reasoning to her as to why she should change a bit ... infact I have also changed a lot for her .... but seems that we are heading no where and I feel lost and heartbroken at times ... as she has started ignoring the stuation rather than resolving it .... Please advise what can I do to keep this realtionship going as I dont want to loose her... howeve, her arrogant behaviour at times forces me to get out of this relationship. I am not sure how to handle this ....