"Ona pracuje jako modelka."

Translation: She works as a model.

[conor.raff]

"jako" is just an adverb here, so it won't decline with the noun following

[rockyderaze]

thank you

[rslife]

Why is "modelka" in the nominative here?

[Jellei]

That's the construction we use with professions. jako (as) + the profession in Nominative.

[PetrDiblik]

Wow, this Polish sentence is exactly the same as in Czech language! :-)