Try explaining things to her in more intuitive terms. She gets to do more damage when her opponent has significant trouble defending themselves. That happens when they have to split their attention across a wide distance (flanked), when they're on the ground (prone), when they can't see where they're being attacked from (hidden), or when you fake them out (feint).

Old hats tend to boil away the actual roleplay from combat, but the rules usually directly support a roleplay-based view of battle. Presenting the game this way had my then-9-year-old picking the game up really quickly.