[goofball]

She knows what's up. She was afraid of the flush and now she's not. She's saying she has a full house and from your description it's unlikely she has 3s full. If she had teh flush she'd have reraised the turn, and overpair she'd have reraised preflop, I'm not sure how a flopped straight would play but it doesn't involve checkraising the river. Her action screams 33 or 77 and there's no way you should 3bet the river.