Humping in female dogs is a sign of dominance rather than desire. If there are new members to the house (feline, canine or human) a dog might be triggered into trying to assert their dominance over their domain.
The dominance theory is outdated. Dogs hump for all kinds of non-sexual reasons - excitement, stress, anxiety, arousal, to initiate play, to tell another dog playtime is over, and because it feels good. If your dog is humping you, she's probably trying to burn off some excitement, relieve stress, or get your attention.