I am so utterly confused by Jenova that I don't even mind admitting it.
I thought she controlled Sephiroth. However, I also thought that he animated what was left of her body, in Hojo's tank, through his will. I don't know how I managed to believe both those things simultaneously. Jeez, it's like a religion.
When did he kill her?
I also thought, but am obviously completely wrong, that she had some kind of intelligence/will that transcended distinctions of cell function - it didn't need brain cells, because it operated like a kind of hive mind in every single Jenova cell, no matter who or what was carrying that cell. Once she's 'dead', do these lose their consciousness/identity but keep their function? Because the remnants didn't seem to think she was dead.
Pondering these mysteries is more interesting than doing my taxes, that's for sure.