My female guinea pig seem to be in heat, but she is not letting the male mount her?

I have one male and one female guinea pig. The female seems to be in heat because she is doing the hip swaying dance, the loud rumbling, and mounting the male guinea pig, however every time the male pig tries to mount her she pees on his face and move away. Im getting scared for my male pig because she keeps mounting him and she is much bigger than him and i don't want her to hurt him. This cant be normal...is it? please help!!!