It isn't aggression and I wouldn't get carried away by calling it "dominance" either. What you can be quite sure about is that it's got nothing to do with sexual manouvres. Insofar as "dominance" goes, it can be a means of signalling status. But when it's either baby puppies you're talking about, or adolescents, then it's very often practice or experimentation with such a manouvre. That is, it's a rather overt and very unsophisticated way of behaving that *most* dogs grow out of. Rather like human adolescents, they tend to be a bit brash and over-the-top in their social interactions, but learn to behave in a more sophisticated manner with time. Humping is squarely in this category. It's something *very* commonly practiced by baby pups, and experimented with by adolescents. The vast majority though, don't carry it through to adulthood, having learnt along the way more subtle and effective ways of behaving.
As for what to do about it - well, dog hierarchies may be one thing, but a dog has to learn to live in a human world. And whatever way you look at it, humping is not a desirable behaviour. That just means you should discourage it, not that you should have a fit over it
Just let the dog know clearly any time she tries it that it's really not cool, and redirect her to an alternative. She will catch on soon enough.
