I conclude from your question that you betrayed your fatherless girlfriend's trust in some significant way: cheating on her, lying to her, hiding important information from her, etc. Depending on the severity of your betrayal, it may be impossible to win her back. Because you two were just dating (not engaged or married), she may have determined your behavior was too big of a risk to move forward. Since dating is the time to discover whether the two of you have similar values, she may have realized you don't and made the wise decision to end it. If that's the case, you should respect her decision, learn from your mistakes, and move forward.
If she's still willing to date you, then you have an opportunity to apologize for your behavior and prove you won't do it again. There's no speedy remedy for re-establishing trust and love in a relationship. This is especially true with a fatherless daughter who may have already suffered an enormous betrayal by her dad. She won't want to get hurt again and will be extremely self-protective like she's wearing a suit of armor. It will take a lot of time, patience, and good behavior to make her feel safe.
The biggest challenges I've faced as a fatherless daughter are revealing my emotions and being vulnerable. If I expressed sadness about my dad's absence when I was a girl, my mother immediately shot down that expression of grief and became defensive. I learned at a young age to keep everything bottled up inside of me. I stuffed my emotions with food as a kid and then numbed them with anti-depressants as an adult. I became convinced that my emotions were wrong and, if I revealed them as I had to my mom, they would be rejected. This false notion caused a lot of damage to my physical and mental well-being and damaged my friendships and romantic relationships.
If she lets down her guard, you can help your girlfriend express herself, so she feels safe, heard, and understood. If you want to have a successful relationship, you both need to open up to one another, be honest about your emotions, and re-establish the trust. Your fatherless girlfriend needs to be secure enough in the relationship to be vulnerable with you.