Law / Polish citizenship eligibility [2]

I am hoping someone can help me find out whether my girlfriend is eligible for Polish citizenship. Her story is as follows:

All 4 of her grand parents were born near Miory in the 1930s which at the time was part of Poland but is now in Belarus. Her grandparents all had Polish birth certificates but only one is still alive. Both her parents were born in this area in the 1960s. At that time this was Belarus but their Russian birth certificates state that they are Polish citizens. My girlfriend was also born near Miory in 1984 and her birth certificate states that she is Polish but she has a Belarusian passport.

We live together in London but she would like to apply for Polish citizenship to make life easier! Does anyone know if she is likely to be successful if she applies?

thanks in advance