This is merely playful dominance, not really oversexualization. Many small dogs exhibit an ego or dominance complex; they meet a new dog or person and immediately try to establish that they, though little, can hump like no tomorrow, aka they are top dog and important. It's an attention seeking issue that may not be resolved easily. The best thing to do to end it is to establish your dominance (not by humping... :) When you play with her, win. When you wrestle, hold her on her back for a few seconds. Most normally adjusted dogs will struggle for a few seconds, then submit, but my bet is she'll squirm till she gets rug burn. It will take time, but you can gradually build her respect for you.
