Sure she didn't object or fight, but the implication was clear she wouldn't give consent. She couldn't say that because arranged marriages are coercive and she had no other options outside killing him. With Reek/Theon right there.
She was however not forced into the marriage. Littlefinger gave her a choice. That doesn't justify what Ramsay did and it doesn't make it anything but rape. But what I don't get is why people are only shocked when it happened and not when Sansa first made her decision, because it was obvious to me that this was the only realistic outcome. And since she isn't an idiot I'm going to assume it was obvious to Sansa too. She deeply hates the Boltons, there's no way she'd ever want to have sex with Ramsay. So what was the expectation here, that Ramsay would agree to never have sex with Sansa? Forget Ramsay, few people in this world would agree to that (bearing in mind that Ramsay was arguably more forced into the marriage than Sansa was, even if he wanted it anyway)
Yeah, maybe Stannis could have attacked in time, but that was probably never going to happen. Sansa knew it too, she told Littlefinger that she'd probably be married when he next saw her. And as satisfying as it would have been had Theon or Sansa killed Ramsay that wasn't going to happen because first of all, they probably didn't have the means, and second of all, they would have been in serious trouble. Okay, maybe Theon would be willing to sacrifice himself to save Sansa but it'd look awfully suspicious if she did nothing to stop this from happening, which would probably lead to grave danger for her (and she's already more or less exposed to Cersei now and therefore depending on the Boltons to shield her). And I don't think I have to say she'd be screwed for sure if she killed him herself. It's possible that she can, probably with the help of other forces, help to take down both Ramsay and Roose, but now is not a good opportunity.
So yeah, Sansa chose the marriage, and while she sure as hell doesn't want this she did her best to endure it. Her alternatives weren't great, but she trusted Littlefinger and would have believed he'd keep in her in hiding had she insisted on that. So she went through with something that she only recently said she'd rather die than submit to, why? Because it's her shot at possibly getting revenge at some point and it's her shot at restoring her family's honor. She's willing to go through something horrible for that end. And in my mind that makes her a lot braver and more determined than people give her credit for.