Why is the perfective verb počkat used here? Telling her to wait seems to suggest a continuous action of waiting.
FWIW, I was introduced to "počkat" as meaning "to wait a little bit." If that's true, we would be asking Žofie to start and stop waiting over a short period of time, which would seem to make it perfective. But someone else could probably give you a more authoritative answer!
Wait, this is Czech to English translation, not other way, your question lacks any sense. both versions can exist, čekat and počkat, but one of them was chosen for you to translate, that's all.