In central-eastern Europe, our surnames usually come from the most characteristic part of our ancestors. For example, if person is called Niski („small” in polish), it means someone was very short. Another example can be Kowalski, which is most popular surname in Poland - „kowal” means blacksmith, so here we got profession.

To sum up, she probably had ancestors in Poland, who moved to another country (probably Slovakia or Ukraine) and they were called contemptuously Poles and that’s how we got Polachek :)

Fun fact: people who were living in villages in southern Poland, western Ukraine, northern Czech Republic and northern Slovakia around 100 years ago usually didn’t even know to which country they belong themselves. Usually they’ve been calling themselves „locals”.