As I understand it, you wonder whether the good months or bad months are more representative of who she is. The bad months sounded terrible. Delaying engagement (1yr?) and marriage (2-4yrs?) seems best for you. In time you'll learn who she is. At the same time, she wants to feel this relationship is building and going somewhere. I worry you will feel pressure and fold after only a couple of months of "good wife", you marry her, and she goes back to "bad wife". Consider what steps you could take between now and engagement to deepen the relationship to relieve pressure. I guess that's complicated by the fact you already live together, know each other's families and friends, are having a baby, etc.--but there must be some steps.
