The different treatment is simple, let's remove the sexual relationships from the equation since everyone has cheated on someone (at least in my playthrough). Rachel has been portrayed as seeing her daughter as an object to manipulate and use. She has lied to her repeatedly, used her as a means to get a business deal done, allowed the stepfather to sound proof her room so that they wouldn't have to hear her cry or yell. At no point did Rachel come across as someone who actually cared about her daughter until at the point when her ex-husband was able to blackmail her into giving up her daughter. Then, once she no longer had her daughter around, Rachel suddenly has a change of heart.
The father has always been portrayed as caring/loving. He supposedly wants what is best for his daughter (beyond just as a good fuck). At no point has he tried to use her as a bargaining chip or to abuse her love for him. He has been constantly supportive. He has quit his job, moved to another area/country, and is helping her become a model. Sure he will benefit from her being successful, but at this point in the story there hasn't been anything about the father that would indicate that he is going to change into Mr Hyde and leave the daughter pregnant and poor in a trailer.
