Look up the Mr Heater line of propane heaters - I've used one indoors without problems.
I'm disposed against electric heat due to operating cost and power failure in stormy times.
A proper gas furnace would be best, I think - sounds like she'd have to run propane if there's no NG service.
Wood heat is dead-reliable, but that means installing a wood stove & maintaining a supply of dry wood.
Whatever you do, have proper ventilation.