USA, Canada / polish people needing visa to visit usa. [8]

hi everyone im new here i need a bit of info ok here goes, my girlfriend is polish and today for the second time she is trying to get a visa to visit her sister in chicago they have not seen each other in 7 years now my g friend is a auntie to a baby boy she was refused a visa in krakow they give her no reason why she was refused this is stupid why no reason does anyone know or is there a way to find out from someone, there are to many stupid rules in this world today thanks really need to know not bein able to see your own sister is heart breaking thank you. franiu.