Jealous of the cat (kinda long)

One of my dogs has just recently displayed jealousy of one of my cats. Cody will snap and lunge at Emmie if they are both near me. I don't understand why she has suddenly displayed this behavior. Emmie and her sister have been with us for over a year and now this. This morning took the cake. Emmie was lying between me and my hubby when Cody just leaped over me and mad contact with Emmie, causing her to sink her claws into hubbys arm and her bolting under the bed. Emmie is kind of the wuss in my cat family and wont fight back with anyone, not even her sister. I don't want to isolate either one of them, which would be the perpetrator of course. Since I have never had to reprimand a dog displaying this kind of behavior do any of you have any ideas on what I can do. I thought about arming myself with the bitter apples. Cody is so well behaved and has never displayed aggression, she's my goofball and very loving, I just dont get it. :(