It's usually the rule of thumb that it's the aggressor that gets removed. In this case it would be Jez.
I think her "brat" behaviour is likely to be fuelled by fear and confusion. She may not realise Oscar is totally blind and may be interpreting his faraway gaze as staring, which would be a form of passive assertion in sighted cats. Also his body language will be strange to her, she's going to need loads of reassurance and extra cuddles from you during these times of transition.
She may also be worried by his scent - I think we established he was neutered only fairly recently? If he still has whiff of TomBoy about him she's likely to be excited or nervous about this too.
In all he's a mystery to her and she's edging her bets by letting him know she's the boss.
Take it easy, let them become familar with one another's smells and sounds, swap bedding around between them, and toys, and when you do allow them to be together be ready to pick Jez out of the way if she reacts negatively the first few times. Eventually she'll grow used to him and when she realises he's no threat might even grow to love him too.
Lots of extra play will help - if she's exhausted she'll be more inclined to leave him alone rather than picking fights, so plenty of da-bird play for Jez. She'll appreciate the time you spend on this too because she knows she's still your special girl when you play together.
