In UK law only a man can be guilty of rape. The "maximum" offence a woman can be guilty of is sexual assault:
"This seems to suggest that the British Government wanted two separate offences because it is believed that a woman cannot physically rape a man. Indeed, it is a common misconception that, due to the mechanics of sex, it is just impossible for a man to be raped by a woman;
the thought is that if a man and a woman have sex, the man must be sexually aroused and so must be consenting. However, even setting aside cases such as where the woman has duped the man as to her identity, men can, and often do, display physiological signs of arousal, including erection and ejaculation, when they do not want to have sex,
Footnote17 just as women can lubricate and orgasm during rape."
Therefore, a woman having sex with a male dog is not raping the dog, because in order for the sex to happen the dog must be aroused and penetrating her.