Heat Pumps and Electric Heating - MIL needs to supplement heat pump

My mother in law has a ranch home on a slab with ceramic tile throughout. The house is heated and cooled with a heat pump but no gas furance backup which is a huge mistake in the Kansas City area. It has been so cold recently that her last electric bill was over $250 for the month. She has a pseudo-fireplace that has natural gas plumbed to it.

How should she supplement her heat pump?

I suggested gas logs but won't they just suck the warm air out of the house?
I've read there are room vented gas logs but I'm concerned about their safety.

Any other ideas besides putting in a gas furnace?

Have you looked into pellet stoves? They are cleaner and a lot less work than wood stoves and more efficient. If you have a space you can put one then your HP will help circulate the warm air to other parts of the house.

I can guarantee there's no way she will burn coal pellets. If she had natural gas installed and put in some ventless gas logs, would this be a good supplement?

Ventless gas logs are a great way of supplementing the heating needs of a home.