。
She was kind to everyone.
Literal
She [topic-は] anyone [toward-に対して][even-も] kind was.
誰に対しても is the universal-quantifier built from the compound particle ~に対して ('toward / with respect to') + も ('even / any'). Question word + に対しても means 'toward anyone, no matter whom.' The ~に対して compound is more formal and explicit than plain に — it foregrounds the 'directed-at' nature of the action or attitude. Without an intensifying adverb, the sentence reads as a flat statement of disposition.