You just have to get 3 good endings from the first 6 (and not do DJ's bad end) and she will be yours! If you've done DJ's bad end you can either reset your files or get every single love point for her (including in the prologue)
Honestly play however you think you would get the best experience! Self-inserting is the design but people absolutely make OCs to go through routes with all the time. Plus even if she isn't romancable if you play as yourself, you can be her BFF! And you can have a more than happy relationship with someone as just friends!
