Mom just barely doesn't qualify for Medicaid. Any suggestions on how I can cope?

Boy my blood boils when I hear something like this. I'm so sorry you are in this position now, and I really wish you would have received proper guidance BEFORE mom was released from the nursing home. You didn't have to be in this situation. I agree with what others have written here, especially Alva's advice.

Is mpm "just over the lomit" on assets or income?

Use some of mom's money to consult with an Eldercare attorney who understands Medicaid in her state.

This is impossible for you to sustain on your own. Use mom’s money and any assets to pay for help now, with an eye toward her moving into long term care. Missing Medicaid just barely means it’s close enough to make it happen. Contact the nursing home of your choice and ask for the social worker or business manager, tell your situation. I wish you both peace

I would place your Mom; spend down will happen very quickly if these are her only assets, and however quickly it happens, that will be the time for re-application for medicaid. If you cannot care for her you may be down to the "ER Dump" in which you call EMS for transport and then refuse to allow your mother to come back to your home telling them you are neither physically nor mentally able to care for her, and cannot participate in her care any more. As you will recognize, if you were not there, Mom would by now be in placement. Do not allow them to convince you they can help, and do not take her back into your home. The Social Worker will guide you through what can be done to place her, and you may need to see an elder law attorney about the assets. Your Mom pays for that advice as this is about HER. That is already going to spend you "down " a bit.
I sure wish you luck. Many people do not have children. They are placed and these things are worked out. Social Workers, sadly for them, do this work and know how to get these things done.
I am so sorry you are going through this.