Parrot increasingly hostile

Sorry to hear about this...

It is fairly common for quakers to change allegiance. Our quaker, Bonnie, tends to target my husband aggressively much more so than myself. But some days it is the opposite.
She tends to keep us guessing.

If you search through the posts on this Forum you will find quite a lot about agressive behaviour - even my posts about our quaker Bonnie might be useful.

Meanwhile you are doing your research here, perhaps you could try withdrawing from Casey altogether for the time being and let your fiance be the "good cop". He could be the one to give her treats. If possible you could arrange a certain time for her to come out of the cage and ensure you are not around at all (you could pretend to go out and your fiance could let her out while you are gone). He could start with 5 mins and give her a favourite treat for appropriate behavour.

When Bonnie is aggressive I sometimes just open the cage door and completely ignore her/disengage from the noise and aggression if possible.
That way I am not engaging with the attention-seeking behaviour.

It's a very difficult situation and we still struggle with Bonnie's behaviour on a daily basis, however, the key is to be consistent in your responses (both you and your fiance) and try to remember that it's a quaker personality trait that is quite common and it doesn't mean she hates your fiance. Try not to take it personally...

Please keep us informed as to your progress.