And she seems to relish the effect repeated teasing in it is having on you, especially since it proves that she was right all along.
It's very humiliating for you, since the forced masturbation in front of her goes deeply against your principles and makes you feel very dirty and ashamed. You know it's your religious upbringing, and now you wish it wasn't so strong, but you can't help it.
That's what led to the argument in the first place, and it's also what Erica seems determined to change about you.