marriage is a commitment. Being gf/bf and marriage is 2 different thing all together. She maybe afraid she will have certain freedom take away, or added responsibility or afraid you piap without condom and have early baby while she's not ready to be a parent. There can be many reasons liek afraid you have more expectation as a wife than a gf. She might also have more expectation on you as a husband. Respect her decision. When she is ready she is all yours. When she is not, you force it won't be good. Don't think so much. You propose 2 year later at 2027 also not late when house is ready.