Truthfully, in my experience, birds 'choose' one person. While allowing all members of the household (as well as regular guests) to get comfortable with your parrot and vice versa, the parrot is still more likely to pick just one.
I would think that having your fiance spend more time with her than you do will hopefully prevent her from becoming possessive of you.
I wasn't even in the market for a conure when I got Skittles. I was actually about to purchase a new computer. But an incident at the pet store one day changed that. Skittles had other plans for my savings.
Basically, when I went up to see him, he dashed down to the bottom of the display aviary in the pet store and proceeded to 'hop' up and down in excitement. Another customer came around to see what he was doing, so I stepped away so she could see him too. He just ignored her and flew back up to his perch and started preening his nails. The lady then made a 'snide' remark ("why is it always the pretty ones that have no personality"). After that lady left, I went back to see him again and he started doing the same thing he did before, only this time he also was rolling over in addition to hopping. I spent a weekend 'thinking' about buying him and making arrangements to see if I could care for him and the entire time all I could think about was how much I wanted him.
I love telling that story cause even after having him for four years, it still amazes me how he came to be in my life. And at the perfect time. I was suffering from severe loneliness and a bad depression. It didn't take him long to cure my suffering.
When I brought him home, he bonded to me instantly. That being said, that is not always the case. It really depends on the person and especially the parrot. Some take longer to bond then others and may bond in different ways.
Skittles, unfortunately, is not very socialized - but not for lack of trying. I live alone and 'rarely' have company and only a few friends. All my family live long distance, so it's me, him and my cockatiel Peaches the majority of the time. So, he is very possessive of me. But not to a point where I can't deal with it. I just can't let him out around other people if they come over. He'll attack them BADLY.