。
She comes down on me really hard.
Literal
She [topic-は] me [toward-に対し] very harshly treats.
あたる here is not the everyday 'hit, strike' sense but the figurative '人にあたる' — to take out one's frustration on someone, to treat them harshly. The collocation きつくあたる ('treat harshly, come down hard on') is the standard frame for this dynamic — common in workplace and family complaint contexts. きつい literally 'tight, severe' shifts to 'harsh' in this context. Note that あたる has a wide semantic range from physical hits (車にあたる 'hit by a car') to lottery wins (くじにあたる 'win the lottery') to this human-relationship sense — context disambiguates.