Is the theory that he drugged her, took off her pants, then she kind of woke up, a fight broke out, and he murdered her? If she had evidence under her nails (per her father's statements), then she definitely put up good fight. Would a groggy person, half out of it on rohypnol, be able to scratch an attacker?
It wouldn't really take much to have DNA under her fingernails or need to be a big fight that she put up. One small scratch could be enough. It was said to be small amounts wasn't it ?