she at first had the same train of thought as you. that paying rent should equate to partial ownership. Granted this house is every bit as much hers as mine except under the law. its really shouldn't be that important. if you two are in love and already talking marriage what do you have to lose? to me if it really bothers you then that might mean you have doubts about your relationship. Had my gf really pursued working out a deal for partial ownership, imo thats a red flag in our relationship.

money is not that important over relationships. moving in and helping out without contracts shows a great deal of trust. Just be aware of whats fair and don't be taken advantage of.