I don't want to show up empty handed so I am looking for advice as to a gift idea.
A nicely packaged selection of tea(s) would probably go down well with the mother, something in tin which be used (perhaps as a tea caddy) for years after the tea has been used. If you give loose tea, be sure to also give a tea egg. Poles drink about double the EU average amount of tea.
her father(he is a military officer and nationalist) objects to her dating outside of Poland.
You sure it isn't your skin colour he's objecting to?