I reckon you're looking at this in too much of a panic. It's not a sword hanging over your head. The deadline isn't tomorrow.

A couple should be working together to solve problems, not against each other. She isn't out to hurt you.

In not telling you the exact deadline, she was trying to balance two things: giving you the freedom to be choose when to marry her, not wasting precious years on someone who won't commit.

It's a very valid fear. Heaps of stories out there about women who wanted marriage or children, and were strung along for 8-10 years by a boyfriend who kept promising them everything in the future.

So. Why do you need to know the deadline? Are you going to buy a ring on the last day just to keep her from leaving? She doesn't want to coerce you into marriage. If you two are on different timelines, it would be better to part ways so that there's no resentment in the future.

If you decide that she's more important than your ideal timeline, what's to stop you from proposing it sooner than later? A ring isn't marriage right away. It's a sign of commitment.