Birds tend to like shoulders for the height, but also because they can run from you when you want to remove them.
I would ban her from shoulders for now. A lot of birds get really cocky when they're allowed on shoulders, so you might just want to nip that in the bud.
I always have my thumb on my bird's foot, so he can't hop anywhere else and knows he is supposed to stay. But I've been doing that with him since he was a chick, and I'm not sure if you want to attempt it just yet.
I always make a sound (for me, a little clicking noise) to let Hane know that I'm going to put my hand in front of him for a step-up. If I don't make the noise, he isn't sure what I'm going to be asking of him and will react with a bluffing bite. And the sound also gets his attention so my hand doesn't surprise him if he didn't see it coming. Perhaps this will help?
You could also give her a treat with one hand, and put your other hand between her and the treat so she has to step up in order to reach it.
I also do step-up exercises (even now, and it helps calm Hane down when he's getting too excited) where your bird is climbing a continuous 'ladder' made by constant step-ups onto each hand.
You don't want to raise up the hand your bird steps-up to, but rather lower the hand you're trying to make her step off of.
IRNs are smart, so I only do about five or six step-ups (max is ten) so they don't get bored and want it to stop, since they might bite to make you stop.
But I really think making the sound before you present your hand and step-up exercises will help. In addition to a ban from your shoulder.
She'll just have to learn to be pet while she's on your hand with lots of attention and treats while staying there.
Some IRNs can handle the shoulder without getting cocky about it (like my sister's IRN) and others just take advantage of it and cannot be allowed on shoulders (like my IRN).
