I have two dogs, both are cross Beagle and Cavalier, and the oldest, a male is 2 and the youngest is 1, a female. 5 months ago, my youngest started attacking my oldest when he was near her food or when we give him more attention. He doesn't retaliate and is scared of her when she does that. She even takes his bones and he lets her. Going near her would make her growl. I believe my youngest has self-esteem issues and wants to be loved, and we do love her. I give her first priority when i go outside (they stay outdoors) kissing her, hugging her all sorts of stuff, then my oldest. But she seems to want all of the attention. When i go to my oldest and give him attention my youngest goes near me. My oldest immediately leaves and does something else. A week ago i have my youngest half a treat, and was going to give her the rest, but gave it to my oldest. She became very aggressive and started biting him. Every time i have to hold her down very tightly or she'll slip out and start attacking him again.
The telltale signs of her anger before she strikes is that she looks at my oldest with complete focus, then attacks. She is smaller than my oldest. He has always been a passive dog, never biting. Even when someone hassles him he bites but not very hard and only to get me to stop.
How can i fix her behaviour?