Oh, if she was using just her mortal form, he could topple her. But she wasn't. Anna's skin heated up, higher than was healthy for a mortal. Her Grace crackled beneath her skin. She slid her hands further up his arms, pressing the back of his hands into the mattress. And pinning him there with her Grace. He was a demon, from what she could tell he was the demon at the time period he came from. But he was still a demon and she was still an angel, the cards were stacked against him. Especially since there was no reason for him to expend his energy fighting against her.
For the most part, up until now Anna had let Crowley wield the power in their little... well, whatever they had going. No, she was just going to call it what it is. Relationship. This little power struggle was Anna giving Crowley what he wanted to get what she needed, this was feeding his ego and letting him have his control despite the fact that it was probably digging herself into a hole. But for the moment Anna needed her own little ego boost.
Anna slid her hips against his slowly, just teasing, intentionally drawing things out because... well, why not. He was pinned for the moment. He wasn't going anywhere, and she had a suspicion he would give her what she wanted, even if he put up a fight anyway (which she expected him to). "You're going to give me what I want one way or another, but if you're good I'll make it worth your while."