The bigger problem with defining Cersei as a fascist is that it's never entirely clear what her base of power actually is. Cersei apparently cows the entire King's Landing political structure into submission with only three allies- her brother, an alchemist, and a hulking mindless zombie the alchemist created. Nobody else even likes her, and she's grotesquely incompetent at nearly anything she tries to do. The only apparent advantage of her being in charge is the legitimacy of the royal line, and even that's paper-thin because she's so far removed from that line and directly responsible for most of the crises that imperiled the royal line in the first place.
The bigger problem with defining Cersei as a fascist is that it's never entirely clear what her base of power actually is. Cersei apparently cows the entire King's Landing political structure into submission with only three allies- her brother, an alchemist, and a hulking mindless zombie the alchemist created. Nobody else even likes her, and she's grotesquely incompetent at nearly anything she tries to do. The only apparent advantage of her being in charge is the legitimacy of the royal line, and even that's paper-thin because she's so far removed from that line and directly responsible for most of the crises that imperiled the royal line in the first place.