I used to steal seats in college. At community
college. I always wanted the coveted back seats so I'd take them if I got there early enough. The most dramatic response I've had is a big sigh. Nobody will fight you because you took their seat. Don't let your perceptions warp reality.
Or you could just tell her to stand her book up on her desk and block your view like back in elementary school if she's really so paranoid about it.