It’s okay to have an understanding before you have a formal engagement.
We dated for about two years while I finished undergrad. He was a graduating grad student from another school when we met. So we were a long-distance relationship, but for most of that period, we had an understanding that we were going to get married. (Not the dumb kind of “perpetual fiance” situation that a lot of people talk about these days, because they think “fiance” sounds better than “guy I’m living with”.) I graduated in May; he formally proposed and we got engaged in late July; and we married in November. But before I graduated, and before he proposed, he did go to my family and express his intentions-- maybe around Christmas before graduation?
You didn’t mention if she was 23 and in undergrad or grad school. Either way, let her wrap up what she’s started, and then let her work on getting a job and an income and see where life takes both of you, in case it uproots you as a couple and transplants y’all elsewhere. I know for us, things were a bit rocky at the start, because DH is six years older than me, and had been living on his own since he was 18. But me, I had never done things like run a household, or stick to a budget, or things like that. I had a lot of growing-up to do… I still have a lot of growing-up to do…
So it’s okay to give her a little time to mature, while you guys get your respective lives organized. You have plenty to do during the course of the year she has between now and graduation-- working, saving money, getting experience, seeing what opportunities open up for both of you.