Luckily, soon after the decision was made, I finally got my first full time job in Finland. I could easily support the two of us and give her an uninterrupted life to focus on grinding up for the math exam. We took the last ~10 years' worth of math exams online, turned their problems into Anki cards, and set her nose to the grindstone. I had had tremendous success with this in college with abstract algebra and real analysis, so I figured the same methodical approach + a very stable living situation was bound to work for algebra through basic calculus.
Five months later, she retakes the high school exam and gets the highest score possible! Her rapid success at this convinced her to give CS a serious try, and indeed her improved math exam was the differentiator - without it she would not have been accepted to the CS program. She got top marks in her first semester at CS as well, I couldn't be more proud. My wife is truly an incredible person.