We sometimes have the same thing in our three dog household. Bailey (our Bassett) is a treat monger. She lets Preston eat out of the same bowl right under her head, let's him climb on her. She will sometimes lie on her back and he will stand on her stomach using her ear as a pull toy for hours. Let me get out the bones or bully sticks though, and she will chase him, bite at him, bark and in general be pretty nasty.
This is a dominance issue. She is establishing her place in the pack. While she may be best friends with Preston, she still ranks higher than him, and if she wants it, she means to get it.
Dogs are pack animals. With that thought in mind, you are disrupting the "pack" ranking by punishing her for "normal" behavior. Be ready to intervene if it gets out of control, avoid the situations that cause the most aggressive displays. Be sure to give Corona her treat first, thereby reinforcing her place in the pack.
Most importantly, make sure your dog always knows you are the pack leader. Do not give them food without making them sit. Give small treats in a group setting, in ranking order, making them sit each time.
The initial few weeks of bringing a new pet into the home is the period where ranking is established.
__________________  Preston  and Paisley have stolen my  |