I'm kind of confused here and I think you guys can help me.
I already looked at the gamescript and I couldn't find what I was looking for.

From my memory Edea sais she found a dieing sorceror of which she received her powers from.
In the end we see a dieing Ultimecia give her powers to Edea.

But some peopl say that Edea already had power when that happened? from another unknown sorceres? where exactly is that said.

I always saw it as Ultimecia being the dieing sorceres from which Edea became a sorceres herself.