I understand your situation. My mother was the same, she stayed alone in her house till her death 2 years before. dad had passed away 5 years before and moms health had deteriorated after that. But she refused to move from there and managed on her own. We are 3 children and I am the closest, which is at a driving distance of 3 hours. I used to visit her whenever possible . We installed an intrusion alarm and a personal emergency response system ( http://www.apialarm.com/medical-monitoring-pers/ ) at her home But at the end of the day I if mom doesn’t pick up the phone when I call her I used to get all nervous.
I’ll suggest you to call a home nurse if your mom is okay with that. That will give you some relief.