Baddies get Steve under mind control--the kind where you're at least partially still aware, a passenger in your own body while someone else takes the wheel. And one of the things they force him to do is overpower Wanda and rape her.

Pick whatever explanation you want for why they do it and why she can't use her magic to fight back. Maybe they've found a way to dampen it; maybe they've just made it clear that if they catch her at it, the next thing Steve does is shoot himself in the head. The upshot is, Steve is holding her down and violating her and beating the crap out of her if she struggles... and she may not have enough access to her powers to save herself, but she's definitely got enough residual psychic ability to get the full running monologue of how horrified and disgusted Steve is at what he's being made to do.

Bonus: The first thing they do afterwards is force him to stand there and take it while they fuck him. Wanda gets a first-person view of that, too--and of how hard Steve's struggling between a reasonable understanding of where the blame for all this lies, and a sick, desperate conviction that he deserves every degrading thing they can do to him.