It is a very strange case but I don't think it's an unduly harsh sentence.
There is a huge level of pre - meditation and deception involved. The victim consented to sex with a man, she did not consent to sex with a woman.
And this didn't happen once, it happened several times. In the eyes of the law she's been convicted of sexual assault and I think lucky to not have been given a more serious charge.
I've been wracking my brains to think of a comparable scenario and what I've come up with is imagine idential twin men A and B. And a woman has met Twin A. She's attracted to him, met him a few times, enjoyed his company and wants to take it further and have sex and invites him over. So one night he comes over to consumate the relationship but it's not twin A, it's twin B but she still thinks it's twin A.
They have sex and have sex a few more times after that. But it's not the twin she consented to have sex with, she consented to sex with twin A and Twin B had sex with her.
She had sex. She consented to sex but the person having sex with her wasn't who she thought she was having sex with or consented to sex with.
I would consider that rape if I was the victim.
And that may be a totally shit comparison but as this is such an unusual case it's what I came up with!.