Instead of acting like a responsible adult and telling the MC to stop, she is letting an 18 yr old underdeveloped mentally emotional boy let him do what she wants with her body. That is a flaw on her part. This is an advantage shes exploiting for her lustful behavior. She needs to keep her inhibitions in check. She likely misses having sex, and hasnt gotten laid in a long time, which explains some aspects of her behavior.
Bella is flawed, its okay. You can still love her with her flaws, but one should not go around berating another character with their flaws when their own favourite character has flaws. Thats what you call a hypocritical mindset.