Please help - I'm a little concerned. We have two bitches (mum and daughter) the mum has started recently "humping" her daughter. Is this normal for girls to do??

Yep! Completely normal!
:)

sounds normal to me my female jrt tries it with my male most of the time,i was worried but ive been told its a normal thing.

I heard, although I may be wrong, that it's not necessarily a sexual thing, but more a dominance thing. So the mum could be trying to show her daughter who is boss. I'm sure someone will put me straight if I'm wrong.

p.s. me and my sister had two female rabbits and mine (the bigger of the two) was always humping her sister. Lovely!

Find bitchers are worse for humping than dogs, think it is a dominance thing.