Welcome to YT
I would say you need to establish yourself as pack leader. She does need to learn to back down.
I have 2 that I adopted at age 2 - they had been together with their previous owner and Roxy arrived there after Bubba & was 2 mths younger - but she established herself as alpha dog - always beating Bubba to the toys - so now Bubba doesn't even play with toys
Work with her or hire a trainer - hopefully you can turn this around - because it is going to be a lot harder if she has to be an only dog & you have to end up re-homing one of your dogs. I am also very concerned she is showing teeth at toddlers. Teeth showing can move to biting.