Übersetzung - Serbisch-Englisch - je donela veoma vaznu zivotnu odluku i sve ce uciniti da je ispostuje

I vote for : "She has decided on a very important decision..."

Hi Lakil,
We don't say in English that we "decide on a decision".
You can say : "She has decided on a very important issue", but for "decision" as a noun, the correct verb to use is "take a decision" (BrE) or "make a decision" (AE)

You are right. I am sorry, I was in rush!
"She has made a very important decision." Thank you.