She should check with her school. They may offer low cost insurance coverage. I had an ex who years ago got her insurance through her college. I don't remember if it covered the year or the semester, but I remember being surprised how cheap it was (pre-ACA).
If you're in New York, check the New York State of Health website, as you can apply through there for state sponsored plans (may be subject to enrollment periods, but domestic partnership may be a qualifying life event not sure).
If you are living together but unmarried, check with your employer to see if they offer domestic partner coverage.
If so, it will typically cost the same as if you were married, or it will be double the single person cost. However, the value of the insurance plan for her will be considered so compensation to you, not a benefit, so it will show up as imputed income and you will pay tax on that amount.
You would have to show some proof of domestic partnership (proof of address, shared expenses, etc.).