As much as you want it to be that way, there is no such thing as long distance caregiving.
Either go to them or arrange for someone else to oversee their day to day needs.
You can phone, you can visit, you can listen to their woes but you can't take care of them from 960 miles away.
You must choose.
Either give up your current life for a time and go to them or give up the responsibilities for their needs to someone else who you hire to be there in person in your stead.
If, as you say, the cancer is spreading and there is no other help you are seeking but what she already has, you need to arrange a trip, before too long, to say all those things you need to say prior to the final goodbye from this life.
I'm so very sorry for your troubles and woe.