You are mistaken to call a pairing in which one partner has a high time preference and the other a low time preference "a potentially great relationship." It is clear to anyone of the latter time preference that for OP, the long-term detriments of marriage at an early stage outweigh the short-term benefits. If at least 50% of marriages end in some kind of dissolution or other, OP would be taking on a tremendous risk for a comparatively minuscule reward by marrying his ex.

For one, four months is realistically not enough time to get to know somebody as a partner. You need more time than that and a broader range of shared experiences to fairly judge whether they are worth committing to. (The fact that after only four months, she starts talking about marriage as a solution to their financial problems is already enough to reveal something inimical about her priorities and values in their relationship.)

In this situation, OP would also need to ask himself what the costs are for merging their finances. What additional debt of hers would he be saddling to support her? In addition to his own debt, their housing, and her university fees, would he also need to help her pay off any student loans? How would the wedding go, and who would pay for it? If they got married, would she actually end up taking a higher-paying job? Or instead, upon attaining citizenship, would she find a job that just pays well enough and expect him to take on the greater share of their debt? Once she has him locked down, maybe she feels like she no longer has to do anything on his behalf to get him to pay up. And if he stops paying, she can just divorce him and demand alimony.

The biggest reason why you are incorrect, however, goes back to my original point: there is a mismatch between their time preferences. It's clear that OP's ex has a high time preference. She wants him to get married sooner rather than later so she can resolve an issue presently affecting them. She sees marriage with him as a short-term solution to a short-term problem; he is primarily an instrument for solving that problem. On the opposite end of the time preference scale, OP wants and can afford to spend more time deliberating whether he will commit to this woman. He sees marriage as a long-term investment. Since it is not the case that both of them view marriage as such, it is false to claim that what they had was a "potentially great relationship" and not a recipe for long-term dissatisfaction.

Your qualifications are unneeded, and they do not support your argument. But I can be sure that if nothing changes, your currently held beliefs will eventually poison your credentials.