In episode 21 of the anime, it was indicated that Meilin was previously an assassin before Sebastian took her in as the maid of Phantomhive household. She used to be a sniper who did not use a scope, due to her sharp far-sighted vision caused by her ill-fitting glasses. She is also physically fit as she can use a sniper rifle like a hand gun and keeps hundreds loaded at once to decrease reload time. It was also revealed in chapter 33 of the manga that she has the same background.
Spoiler: end of 1st season
At the anime's conclusion, it is unknown whether she is alive or dead, although it is noted she was breathing before she collapsed.
|Kuroshitsuji II||Season 2||TV||12||0||0|
|Kuroshitsuji II Specials||Special||Special||6||0||0|
|Kuroshitsuji Picture Drama||Special||Special||1||0||0|
|Kuroshitsuji Circus Hen||Season 3||TV||10||0||0|
|Kuroshitsuji: Book of Murder||Side story||OVA||2||0||0|