You don't mention exactly how much less than $15000 her annual income is (this definitely makes a difference) but, assuming that it is between $11490 (100% of the federal poverty line) and $14999, she would likely qualify for subsidies that would cover almost the entire cost of the premium with her share being as little as 2% of her income.
I would suggest visiting https://www.healthcare.gov/
on or after October 1st to explore what specific options are available to her. That site may also be able to refer you to a professional health insurance "navigator" that can provide personal assistance.
However, for those at these low income levels, the costs of the premium after ACA subsidies and the potential out of pocket costs (someone who makes $15000 a year would likely find it very difficult or almost impossible to afford a $300 annual premium and $2250 in out of pocket medical expenses) could be too much which is why the ACA (before being partially gutted by the U.S. Supreme Court decision in National Federation of Independent Business v. Sebelius
) expanded Medicaid coverage to include them. I really do not understand why the federal government can't just take over Medicaid in the states that don't want to expand it. Of course, doing that would likely require new legislation and potentially cost significantly more without those states covering any of the additional costs but surely they could figure out some way to cover at least some of the very poor using the funding already approved by Congress. Unless we change the current system to deny without exception any emergency care at no cost to the very poor (such a decision would likely significantly increase the mortality rates of that population), taxpayers and healthcare insurance purchasers will still be paying for very expensive emergency medical care for that population.
I also live in a state (Texas) that has chosen not to expand Medicaid and I can certainly understand why rejecting Medicaid expansion funding appears to be fiscally prudent since it would still result in the state eventually paying 10% or more of the additional costs. If you want to keep taxes low and have a balanced budget (which is required by the Texas Constitution), accepting federal funding to expand Medicaid could be perceived as a huge risk when it would commit Texas to spending billions of dollars it doesn't yet have. However, some of those who have crunched the numbers
have determined that it is fiscally irresponsible for Texas to reject federal funding that would likely significantly reduce the amount Texans are already paying for indigent emergency care. But I digress...
You may also want to research local healthcare providers and community clinics that currently provide free or very low-cost medical to the poor and the uninsured. These publicly and privately funded organizations exist in most communities in the U.S. and provide somewhat of a safety net for those without any other viable options as many communities have recognized that it is fiscally prudent to provide free healthcare to the indigent in a non-emergency setting while failing to do so can result in exponentially increased costs for preventable emergency care and disability services funding. You might also consider researching whether any of the medications your mother needs are covered by programs (primarily funded by pharmaceutical companies) that provide free or very low-cost prescriptions to those who need them. Many of the most widely used drugs are covered by these programs.