「あ、は、はい・・・ごめん、玲姉」「コラ。幾ら親戚とはいえ、私は先輩医師よ？院内ではちゃんとケジメをつけなさい」

「、、・・・、」「。、？」

"Ah, y-yes... sorry, Sis Rei." "Hey! Relatives or not, Im your senior physician here, got it? On hospital grounds, you need to keep things properly professional."

Literal

"Ah, y-yes... sorry, Rei-sister." "Hey! However-much relative [even-though-とはいえ], I [topic-は] senior-doctor [assertive-よ]? Within-hospital [at-では] properly boundaries [object-を] attach-[imperative-なさい]."

Hospital setting; familial vs. professional boundaries. 玲姉 (Rei-nee) is a familiar form of 玲姉さん, a younger relative's way to address an older sister or cousin. コラ is a scolding interjection ('hey! cut it out!'). 幾ら...とはいえ is a concessive 'no matter how much X, even so ~.' ケジメをつける = the set idiom 'to draw a clear line, establish boundaries, distinguish contexts' — a quintessentially Japanese concept tied to うち/そと context-sensitivity. ~なさい is a soft imperative (teacher/parent register), less harsh than the rough imperative.