Female lab fleece afgan?

I have a 9 month female lab that loves to hump my fleece afghan. She doesn't bother anything else, none of my husbands things just my afghan. We had her spayed at 6 months of age. My husband says I am the "alpha" in the family as she listens much better to me. Two school of thoughts I have come across. 1. She is showing affection and 2. She is showing dominance. She is a very gentle and lovable dog. Any opinions on this behavior?