These are my two dogs, Zoe on the left, Wendy on the right. This is a rare picture of them together in calmness.
Zoe is "big dog" between them, but Wendy wants very much to be "big dog." I believe that Wendy is plotting to take over the world, but her immediate goal is to take over the house, starting with Zoe. When they're both awake, not 30 minutes goes by where Wendy does not attempt to bite Zoe on the scruff, or take away some toy that Zoe is guarding. (Zoe tolerates this for about thirty seconds, then lays into her to re-assert her big-dogness.)
The biting thing is not restricted to challenging Zoe; Wendy is a toothy little girl. She loves my shirts, especially dress shirts, because she can pull at the buttons. If I leave a shirt in reach, and she is a very long dog so she can reach far, I will find the shirt later with dried slobber and tooth marks around each individual button -- and sometimes tooth marks where a button **used** to be.
To boot, she's a little butter-thief. If I leave the butter out and uncovered, I will come back to it to find the butter-knife displaced and the butter itself with a big curvy section licked out of it.
She's good when she's not naughty, but she is **so** naughty. It's good that she's cute, otherwise there'd be a problem. ;-)