Nothing is normal, dogs are strange when it comes to humping, she may be exorcising her pecking order, mine did the same to my sisters bitch, infact looking back she was extremely randy about the same time. Dogs are strange and wonderful creatures.
mine have all humped each other near the end of pregnancy, my daughters girl had puppies 7 weeks ago & mum is now having to be kept seperate coz she is humping them,
thanks everybody advice most apprecated .poor girl dont think she's got the energy to hump just now she's looks like a baby elephant not long to go now