Can you retroactively be charged for health care if you loose insurance?

Kind of a state specific situation, so I’m hoping someone has some insight. My GF is self employed and has previously qualified for MNSure under MNCare, Minnesota’s ACA system. This last year (2023) her income was too great to qualify her for MNSre, but as a small business owner she just completed her taxes and just found this out yesterday (October 15). So she will be loosing her insurance, and is freaking out that it will retroactively include the current medical year. (And of course she was diagnosed with breast cancer earlier this year, so her potential medical costs are huge). The paperwork she has is not clear when the policy will get cancelled. She thinks it’s immediately, I think it’s probably that you can’t renew coverage for the next year. She’s also concerned that even though she didn’t officially know she had too much income until she completed her taxes, she’s had the income for the year and that they will therefore retroactively cancel her insurance to the beginning of the year. The generic information also says she *may* have to pay money back if she doesn’t alert them to a change in her income. Thoughts? Things we’re missing or need to take into account?