After her last relationship 2 years(iirc) ago, Holly is average girl, knew nothing about things than she had at that time, no personal growth, than Holly is head over heals in love with Ian and met 2 girlfriends who like to spend time with Holly and vice versa, who also happen to be making Holly more comfortable towards different things included sex, than Ian is not interested/invested in Holly as Holly is in him, Now Holly is more confident, open to try new things/experiment, curious, and trying to make up for the time she lost by turning into a Sigma Girl why people think she is slutting herself out or Holly is just despicable. This thought is just absurd. She is adapting, changing to accommodating herself to make her better than her previous self who was only nerdy and knew nothing about her body, dressing sense and so on.