"She impressed me."

Translation: Zrobiła na mnie wrażenie.

[lucanin]

Dlaczego nie jest poprawną odpowiedzią- Ona mi zaimponowała

[Jellei]

A bit different shade of meaning (for example 'zrobiła wrażenie' may be because of what she did, but also just because of how she looked, while 'zaimponowała' should be because of her behaviour and actions and not looks), but it's the same word in English, so should be accepted. I reported it.

[blairecoucher]

Why is "na" required? I searched this on Wordreference and it only says "robić wrażenie" or "imponować komuś." Is the preposition only required there is a direct pronoun?

[Jellei]

Yes. Something can be generally impressive, so "robi wrażenie", but if it impresses someone, than it "robi wrażenie na kimś" (taking Locative).