"Pomagałam jemu w pracy."

Translation: I was helping him at work.

[Szparag]

"Pomagałam mu w pracy" sounds much more natural.

[SnowyKnigh]

And more correctly, shorter form shuld be after verb and longer before verb (I am from Poland, I live there. Im here (checking this coure) to check it, or just trying to check it, so im better in polish than english). Sorry for mistakes in my comment (english ortography etc.)