why is she aggressive

Question
Hi i have a female staffy named ruby that we have had for 6 years and we have just got a male staffy named dex who is 2 years and he is constantly trying to hump her and she is very aggressive towards him but if he isn't trying to hump her they are fine together do you think that she may be pregnant and this is why she is aggressive towards him when he try's humping her.

Answer
Hi Jade. A lot of times humping has nothing to do with breeding. It's a way to express dominance. It sounds like that's what is going on here. Your male dog is at the right age, and intact I take it, to show dominance. He's trying to dominate her, and the reason she's aggressive towards him is because she thinks that she's 'boss'. She's trying to show him where he stands. Sometimes, dominate females will also hump. Sometimes you have to let them sort it out for themselves who is alpha, just don't let it get out of hand. If it starts to get messy, you may want to enlist the help of a trainer. Above all else, you need to remind the dogs everyday that you are the real alpha.

Another reason that females get aggressive is because they are in heat. Is this a possibility, or has she already been in heat recently?