I would bet that she had a teenage orgasm when she felt daddy's cum spurt inside her tight vagina. At that point, there was nothing but the absolute intention of achieveing as much sexual pleasure from committing ince*st that she could . Nothing else mattered to her.
Some people may think that this kind of activity is uncommon but it is more prevalent than they would expect. Most girls would be reluctant to divulge their sexual affairs with a stepfather or a father because they consider it a de*praved act of lust. However, these same girls will continue having sex with their father because it feels extremely erotic and so wonderful to have a man's cock in their pussy. The taboo implications of ince*st also excite a teenager's mind to the point that repeated sessions of intercourse are considered "real" and required by them to achieve womanhood.