Learn Polish: Niedawno pracowała w kawiarni. - She recently worked in a cafe.

In the Polish past tense, verbs change their endings based on the gender of the person doing the action. The -ła ending tells us a female is doing the action. If it were a man, it would just be pracował.

The translation says "She recently worked", but there is no Polish word for "she" (ona) in the sentence. Why?

Because the verb pracowała already has the feminine past tense ending -ła, it's obvious that a female did it. In Polish, it's very common to drop pronouns like ona (she) or on (he) when the verb's ending already gives away who is doing the action.

Why does the word for cafe change to kawiarni here?

The preposition w (in) requires the following noun to be in the Locative case when talking about a fixed location. The dictionary form is kawiarnia, but it drops the final "a" and becomes kawiarni to show where the working happened.

How does the word niedawno get its meaning?

It is made by combining nie (not) and dawno (a long time ago). So literally, it means "not a long time ago," which translates perfectly to "recently."