This is the 9181st most frequent Polish word.
słowaczka
A Slovak woman.
The word 'Słowaczką' here is used to denote Maria's nationality and is in the instrumental case due to the verb 'jest' (is).
Maria jest Słowaczką i mieszka w Bratysławie.
Maria is Slovak and lives in Bratislava.
In this sentence, 'Słowaczkę' is in the accusative case because it is the direct object of the verb 'znasz' (do you know).
Czy znasz tę Słowaczkę, która pracuje w naszym biurze?
Do you know this Slovak woman who works in our office?
Here, 'Słowaczka' is in the nominative case as it is serving as the subject complement in the sentence.