I agree with much of the advice you've received but have to say a couple things based on my own experience. One is that at this point, I wouldn't recommend your SO have anything to do with your little girl. And I most certainly would not suggest leaving him alone in a room to interact with her until he's had experience handling & interacting with birds. Does he even WANT to interact with her or only to please you?
She has been through way too much in her short life time & deserves to be doted upon for a while with just you & get to trust that you're not going to go away or move her ito some unhappy place again before she should be expected to start learning to trust someone else...IMO.

And I think maybe you might have an unrealistic expectation of just how long that can take.
My story, as short as I can make it. Angel, my semi-rescue Goffins, turned against me shortly after I brought her home when I moved her cage to the family room & out of the bird room thinking that if she were removed from the vicinity of my other birds & I brought them down one at a time to play with across the room from her for brief periods, she might eventually come to see that they weren't going to harm her & she had nothing to fear since she'd had a bad experience with a Grey in her previous home & was terrified of all other birds.
Instead, she apparently came to see ME as the same as the other birds & became totally terrified of me. It broke my heart. She remained in love with my husband (she'd loved me too during the brief period before this), but my husband is most definitely NOT a bird person & has never had a desire to learn to be one.
It quickly became apparent that this was going to take a very long time to overcome, Angel's fear of me, not Rob's aversion to birds which isn't going to change. And this is how I came to own two Goffins.
I missed that Too interaction & the relationship I'd had with Angel briefly so much that I didn't think I could take seeing her so terrified of me & knowing that it might be years before I won her over again. So I brought home baby girl Audrey & that worked; I was able to have my Too to love on which made it bearable to keep Angel & give her the time it took for her to learn to love & trust me again.
It took more than FIVE YEARS. But she adores me totally know & is an absolute cuddle bug. During that time, I never forced her to interact with me. I never tried to make her step up or touched her in any way. I kept time spent near her to a minimum several times a day since it terrified her so & kept busy when nearby without looking at her or making eye contact but taking softly to her while making bird toys or watching TV for instance. I tied a rope from the top of her cage to the back of my desk chair so that if she ever wanted to approach me, she could. And eventually she did. First it was just putting a foot on the rope without leaving the top of her cage; I could feel the rope move slightly whenever she got on it but never turned around to look at her. This went on for a few years. Two steps forward, & then one step back. Over & over.
Your situation is much less extreme & your little girl sounds more angry & mistrusting than fearful. I wouldn't recommend goint to the extremes I did & avoiding contact, but please do give her whatever time (& patience, no scolding or punishment) it takes. Birds are prey animals. They are victims of predators in the wild. They are hard-wired to be cautious & wary of anything & anyone who has violated their trust & to be reluctant to let down their guard. It's just self-preservation.
But back to your SO, your baby might very well be jealous of him & the time & affection you give him. She may see him as a threat to taking you away. If so, leaving him alone in a room with her could very well worsen that perception & the jealousy & make it impossible for the two of them to ever get along. It really isn't necessary that he have a relationsdhip with her, only that you form a healthy, trusting one with her again.
Boyfriends, girlfriends & even spouses come & go no matter how much we think they won't. Children are forever. And I think we owe it to these precious little feathered lives we've assumed responsibility for to view them in much the same way & keep & protect them unless circumstances beyond our control make it impossible for us to provide them with a physically & emotionally happy & healthy environment.
Just my two cents.
