Sounds like she's just trying to make you feel bad .. And she succeeded. You have to do what's right for you and your family first. If she can't understand that .. She's not the right girl for you.
You're not a douche.
But I know what it feels like to be an insecure woman. Maybe reassure her that you care for her, but truly need some space for the reasons you listed.
It certainly would not hurt. And it would put you in the position of walking into university with Junior standing some day, if you were to choose to do so.