"Wczoraj mi powiedziała."

Translation: Yesterday she told me.

[conor.raff]

regular past tense, following the stem "e" - "a" rule (with the regular exception of masc. pers. plurals)

"Verbs with infinitives in -e change e to a in all forms except the masculine personal plural."

Swan, Oscar (2008-10-12). Polish Verbs Essentials of Grammar, Second Edition (Verbs and Essentials of Grammar Series) (Kindle Locations 1339-1340). McGraw-Hill Education. Kindle Edition.

[va-diim]

"She has told me," is present participle, occasionally, in the past. It's imperfect. "Yesterday" doesn't belong.
"She told me yesterday." This is past perfect.

[Jellei]

Versions other than with simple "told" deleted. Thanks for noticing.

[va-diim]

Cool! I feel like a real contributor now! Dziękuję!

[JerryMcCarthy99]

Actually, "She told me yesterday" would be more natural English than "Yesterday she told me".

[purpurowypieprz]

How would "yesterday he told me" look like?

[Jellei]

"Wczoraj mi powiedział".