It's very sweet and noble that you want to help your girlfriend who's a fatherless daughter. But, let me give you a word of caution that I also give to my teenage sons: “When you rescue a damsel in distress, all you end up with is a distressed damsel.” Some men (kindhearted but foolish) fall into the trap of choosing a woman who needs to be “fixed.” That, however, is an impossible task. The only one who can fix her is herself. She must be highly motivated to change and willing to do the hard work—possibly with the help of a good therapist. Sometimes a fatherless daughter wants to stay in her victimhood and let it define her. It will be her identity throughout her entire life so please proceed with caution!
With that being said, you can encourage your girlfriend to do things that will build her self-esteem. With a healthier self-image, she won't be wallowing in the pain of being a fatherless daughter or wanting to fill the hole in her heart by getting married at a young age. Building her self-esteem is not some airy-fairy notion but involves taking concrete steps. You and she, for example, could tackle some goals together that involve getting in shape and learning new physical skills: training for a marathon, taking ballroom dancing classes, hiking to the top of a mountain, learning to ice skate, or pumping iron. You and she can tackle some ways to improve your mental well-being and career prospects by taking college classes together, joining a book club, or attending events at your local library. You and she can look outside yourselves and help others by volunteering at a homeless shelter, the SPCA, or a local elementary school. You and she can find peace through meditation, praying, attending religious services, and being in nature. By pushing herself and achieving goals, she will become stronger in body, mind, and spirit.
You sound like a caring boyfriend, and I wish you much luck in your relationship. Since one in three women identifies as a fatherless daughter, there are a lot of us damaged souls out there. If your girlfriend is motivated to move forward in her life, I think the two of you will be just fine. If she keeps slipping back into the hurts of the past, then that's a serious issue. You may need to end the relationship and ask yourself why you're attracted to a woman who needs fixing. You don't want it to become a pattern.