I understand what you are saying. I thought so too. I see it as follows:
1.- In the first scenario, Victoria blackmailing Audrey to fuck a stranger (who is actually the MC, her brother), the clear victims are Audrey and the MC. Audrey realizes, Victoria would feel no remorse in doing so. She would be happy or even give a damn. Meanwhile, the relationship between Audrey and the MC would be on the rocks thanks to this while Victoria could try to let them know that it's not so bad and Victoria, thanks to her being a blackmailer and a shitty friend, would be left as the "heroine" of the story since thanks to her, Audrey and the MC accepted her feelings. And this would be Victoria's bullshit pretext for the MC and Audrey to forgive her. "Sorry for blackmailing your sister into fucking you. I feel terrible, but it served to make you guys realize you're in love." Victoria might look like a victim, but she would be an irredeemable victim for what she did.
2.- In the second scenario, Victoria fucking the MC making Audrey look at them, seems to me a more redeemable scenario for everyone. The MC would still be a victim, Audrey too but to a lesser extent and Victoria would come off as a shitty friend, but not a blackmailer. Also, Audrey would keep her virginity as she wants it for a special person on a special occasion. (Also his brother. But this time being aware of it and genuinely wanting to do it) This would be a sincere pretext for Victoria to truly redeem herself. "I fucked your brother to give you sex lessons. I screwed up and I am genuinely sorry. But hey, at least I didn't blackmail you into losing your virginity to a supposed stranger."
I think both scenarios are strong enough to create the necessary drama. Both have their pros and cons. But, as I said, I personally think the second scenario is more redeemable for everyone.
If we look at it negatively, it's basically "I blackmail you into secretly fucking your brother because I want to help you but I'm a blackmailer and a shitty friend" or "I fuck your brother without you knowing while forcing you to watch so you learn because I want to help you but I'm a shitty friend."
Anyway, that's my way of looking at it. I find more pros to the second scenario than to the first.