Please Stepdad? I Never Ask For Anything!

My stepdaughter has always done really well in school. She's a naturally smart girl and has a lot of potential. I consider myself to be a vital part of her life since I teach one of her classes at school. I don't expect my daughter to be perfect, but this past semester hasn't been her greatest. Because she's so close to graduating, I think she's been slacking in school.I only want what's best for my girl, and I tried to reason with her before and tell her that going to summer school is no big deal! For some reason, she seems so ashamed to not be able to graduate with the rest of her class. It cuts me to my core to hear her call herself stupid and say she's not good enough. Maybe she can't see it, but she is a very bright young lady! 'You can do anything if you put your mind to it,' I told her, but she's just as hard-headed as her mother.In an effort to help with her grades, I've been encouraging my daughter stay late after school. She can improve her grades if she wants it bad enough. But after she puts me in a tough position, I have to question my relationship with my daughter...She looks at me with her big blue doughy eyes, and begs me to give her a passing grade. It's impossible to say no to her, even knowing that by doing so, it would not be in her best interest.Daughters always find a way into their father's hearts, but my daughter figured out a way to get into my pants. Despite how much work I put into helping my daughter in her classes, she still manages to get her way. I promise her a passing grade, but she has to promise to not to tell anyone about this..