Is sex only once every 4-6 months normal?

My girlfriend won't have sex with me. She claims she's interested in me and attracted to me but when I try to initiate she refuses or starts and argument. She says having sex only one time every 4-6 months is normal. I love her and I know sex isn't love but both sex and love are important. Is this true because it sounds hard to believe and I'm starting to have thoughts of leaving her due to this.