Now this is an idea just to have a brutal experience inflicted upon a very nice girl. And I know some of you like that! The rest would rather have rape and abuse be some sadistically delightful instrument of poetic justice...Well, I just don't do that scenario.
The victim is young, sweet, and hosting her engagement party! She's wearing a soft, pastel gown--pink, mauve, or light blue, Very long, very full-skirted, and very delicate and feminine. I suggest a summer-time setting, and it's a light satin, with a sheer over-lay. The bodice is satin, and somewhat snugs over her not-yet-mature breasts, with spaghetti straps, but there is a sheer over-blouse and full, sheer sleeves leading down to ruffled cuffs.
A spurned suitor (possibly lower class than she and her fiance) crashes the party and asks, begs, to have one last word with her. He hopes to get one last opportunity to plead his case, but she wants to make him understand she will not change her mind.
You've got a psychological reality here: a spurned lover is most likely to be dangerous when he realizes that his situation is completely hopeless (think:O.J. Simpson). If you want the victim to be "deserving" of her fate, you could make her cruel and insensitive in turning him down. I would rather she sweetly, innocently tries to have him understand that he will have to get over it and look for another.
Which he will have no part of! He clamps a hand over her mouth and drags her out the back door, to the garden, and then back behind the tall, thick hedges, where he will (1) "possess"* her, at least this one time, and (2) despoil the winning suitor of his beloved's oh-so-precious virginity.
She is too confused and ashamed to tell anyone, so she puts herself back together and returns to the party an hour later, pretending that nothing is wrong.
*as a period piece, one could use all sort.s of archaic terms