@Elliandre , it seems you were right that the fire is starting when she throws the tablet down in front of the chair. I had one more fire since my last post, and this time I did not get over there until the tablet was completely destroyed. It was a pile of ashes between the chair and fireplace.
I moved the chair back just a teeny weeny bit more making it about 1.2 tiles away (1 full large tile and about a half of the small quarter tiles) and took the advice from above to turn the chair away from the fire a little more. No fires since....at least not yet.
Thanks for people who offered help here. I use fireplaces often and I was sure that chair was not "too close". 1 full tile is always enough distance, at least with the fireguard upgrade, in every household I've played for years.