I had a beagle and malamute/golden retriever mix at the same time.
I had the big dog first. But he was huge - grew to weigh about 120 lbs and my son, who was about four at the time couldn't walk him and he wanted to have a little dog that he could walk when I walked the big one.
So a friend of mine had these beagle puppies and we got Joshua. Joshua never settled in. Even though he had had his doggy friend, my other dog who was very well behaved- and the opportunity for a very nice dog life. I never did get him house trained. I've had dogs my entire life and have never had this problem with another dog. We had a large fenced side yard - more than half an acre for him to run around and play with our other dog on - but he was constantly digging under the fence and getting out.
I finally gave him to the guy who was rebuilding our chimney as he was a hunter and had hunting dogs and a bunch of acres out in the woods for Joshua to roam freely on. He didn't have any problem with him at all.
I guess the moral of my story is that the other dog didn't help. And I would never get another beagle- no matter how cute it was-and it seemed like what this little beagle needed was space to roam.
But I just reread your post - and if this behavior is new - maybe she is bored and could settle down if she had a friend.
I've had as many as three big dogs at a time with no ganging up.
Maybe I've been lucky - all of my dogs except Joshua have been really well-behaved.