Poland = racist skinhead country of the new era...
also with generalisations like this you are not going to be very popular with her family, no matter what your faith is...
you wouldn't like to be called a terrorist, only because you're muslim...
as to your gf. at the very end it is not up to you yo ask her to let her family behind. it is completely her decision and your role in this is minimised to being there and support whatever decision she makes... once more communication is key here. where are you going to live? what happens when you have children? etc.
it might well be that her family changes their minds once they see that you treat her daughter well.
my gf's family was sceptical when she started dating a german. the family realised though that her behaviour changed in the last year (we both live in the uk) and when they finally met me they accepted me immediately because i treat her daughter miles better than any of the previous bf's...
time might tell a different story here as well...