Hello, I guess it's a joke. Maréchal is a marshall in the army, and when we say someone is "aux fourneaux" it means he/she is in the kitchen cooking. So I guess a "maréchale des fourneaux" is a kitchen queen or kitchen boss, or kitchen goddess or something like that. It may be a pun too as "maréchal des logis" is a rank in the army (a low level rank) so maybe it means that she just commands in the kitchen…

Thanks a lot)