Even if you tell her not to come, she'll come anyway.
Literal
Come-[negative-imperative-な] [quotative-と] say-[even-ても] she [topic-は] come-[emphasis-よ].
~と言っても ('even if you say') combines quotative と + 言う + ても (concessive 'even if'). The quoted content 来るな is the plain negative imperative. A characteristically Japanese way to frame 'even if you tell her not to.' Compact and natural.