Green Cheek hates my mom

[Kouken]

My green cheek hates my mom and I'm not sure why. In the past he used to be alright with her and didn't mind her but now he HATES her. He gets mad if she is near him and will try to bite her if she makes eye contact. (He will however fly to her if he is being bad and doesn't want to go back in the cage.)

I don't understand his mood change. I'm pretty sure my mom never did anything to him. The only thing I can think of is that my other parrot who he adores loves my mom and my mom is always taking her away (out of the room to put on her) from him. Could this by why?

 

[hacatta]

My first green cheek hates my mom too,but it is her fault trough,she liked teasing her and well 3 years later she still holds a grudge.
Did she change anything?hair for example.
My sister has pink hair,ever since my moms bird are deathly afraid off her,it's been 2 years now(and yes still pink).