No electricity= o pellet stove

Go to csia.org to find your nearest certified chimney technician to help with options

No electric pellet stove

https://www.homedepot.com/p/US-Stov...ravity-Fed-Pellet-Stove-GW1949/206691061

Not so

Battery backup.

The only thing I would offer is that you use a single wall flue. A two or three layer will lower the temps on the outside of the flue but will rob the heat from the inside.

On which to get for me would center around access and cost to wood. It sounds like pellets in many cases is cheaper to operate.

You didn't consider relocating the thermostat after the stove was installed? That's such an easy low-cost solution to such a problem.

The battery power solution choice is what will fail her. She will have the stove and pellets, but no power. If she's not able to start up a small Honda inverter generator, or care to own one (which is extremely easy), it's unlikely a set of 12V batteries will be maintained at the ready and functional when really needed. They eventually die even when not used, so a regular test & replace program would need to be followed. The small generator needed weighs less than some gals' suitcase and is easily started. You can have 3 or 4 gallons of the "canned fuel" available to fuel it. (That stuff lasts for years.)

As a test, I just asked my wife her choice between the two. She's learned how to deploy our much larger generator and isn't intimidated by the process. She said she wouldn't like to have to take care of or hook up batteries.

As I stated, it was a house we were RENTING!

I took that as you were renting it to others. Now I get that rented it from someone else.

LOL - I would never be a slum lord. That house was, um, unique. The water heater was under the stairs, boxed in, behind the refrigerator in the kitchen. It blow as we were moving out. What a hot steamy mess. We didn't know where all the hot water was coming from.

Bottom line. I am going to do whatever I need to do to make my little girl happy. She wants what she wants and she is aware of all the scenarios and what if this and what if thats. My job is to get her a pellet stove, battery backup system, installation.

I need to figure out the right one.

Looks
Affordability
Efficiency
Safety

Battery Backup system. She is a stickler for routine and detail, so keeping up with a couple batteries and a way to be sure they are charged and still work is no issue. Guys, we all maintain 3 or 4 batteries on our boats and deer feeders , phones, everything now days has batteries and chargers and back up batteries Geez , you guys are thinking a battery backup system is some out there crazy way to turn a little bitty screw that peddles little pellets thru a fire box is going to be hard to prepare for? It wont need to work but a week. If it quits working she has family friends neighbors and good old Country girl willpower and common sense to get her by. I'm not talking end of the world days.

We had a pretty nice upper end pellet stove in Washington State .Learned to keep a small wet dry vac handy with a real fine filter in it to clean out the ash . We ended up removing it and putting in a Vermont casting direct vent free standing gas stove . It was super quiet and didn't have to have a fan running just to operate . I will never have another pellet stove after having the free standing gas stove operating off a thermostat .

What was the gas source? Propane bottles plumed into the house? Her house is all electric.

reel, just google pellet wood stove and start shopping. get her what she wants as she sounds like she is not helpless.
do your research and go for it.