Can my girlfriend kick me out even though I pay her $600-$800 per month?

From what you have written, it seems as though you are on a month-to-month lease with your girlfriend where she essentially is your landlord concerning the unit you are occupying with her. Since she is your landlord and since she wants you to vacate, she can serve you with a 30 day notice to vacate assuming you are on a month-to-month lease legally.

If you refuse to vacate even though you are willing to pay the requested rent, she can still evict you via an unlawful detainer action filed in the county court house where the rental is located.