Yes, female dogs do 'hump'. My rhodesian ridgeback humps my male Rottie quite frequently. I thought she was having an identity crisis when it first happened. But, learned quickly that even females do this.
We literally had a chain of dogs humping each other in my back yard one night. My niece had her 'boggle' (Boxer and beagle) over, he is male, Kahn was humping Copper, and then Kiah jumped on Kahn and was humping Kahn. I Only wish we had a camera out for that funny moment. We laughed so hard,it was the funniest thing I had seen in a long time. We still laugh about it!!
I would let her know that it is unacceptable to hump mommy however!!
