As seen in the original depiction of Ms. Mercy Grace Luthor in the Supergirl (Mom) & Supergirls vs NinjaGuy Series..
Birthdays n Hijinks : [link]
And in the following depictions ...
Ms. Mercy is the Chauffeur & family bodyguard to the Luthor Family Clan and Confidante & Closest Friend to Linda Lee Kent whom had saved her life when she had arrived into Smallville years ago, living a miserable, destituted transient existence from town to town, homeless, hungry, with nobody to call as friends, no home to rest and with no meaningful purpose in life until finally rescued by the young Ms. Kent in the darkened, empty streets utterly exhausted, emaciated, road-dirtied & nearly at the end of her tethered, harsh life.
-It was young Linda Lee Kent whom finds Ms. Mercy already collapsed in the grimy wet street gutter and Linda had flagged down the dashing Lex Luthor in his fancy red car.
They take the dying Ms. Mercy with them to his mansion where they get young Clark to bring their specially equipped rocket ship to heal Ms. Mercy's deteriorating & dying body and help her slowly recover from her nearly final death ordeal.
-As time passes and Linda nurses Ms. Mercy to health in Lex's Mansion on her freetime, there grows a bond of friendship & trusting love between the two that Ms. Mercy vow to replay back both to Lex whom took her in and Linda whom saved her.
-Ms. Mercy's health recovers & blossoms under Linda's care and she grows up on Lex's Mansion Complex and eventually trains herself to become a tough, muscularly lean, mean fighting machine to become his personal bodyguard and also quietly trains & protects both Clark & Linda so that they can prepare themselves for the rough & tumble hostile environment of real life that she had endured & experienced...
-When Linda inexplicably gains her extra five daughters thru that unknown madman's actions years ago, Ms. Mercy lends her tough love, her lively assistance & experiences and becomes their overall trainer, teacher & protector for the often bickering four daughters of might of Mrs. Linda Lee Kent Luthor & her large family.
Ms. Mercy Grace Luthor also has a daughter by Mr. Luthor ; Ms. Linda Mercy Luthor ; in this depiction below
Her history is explained in the body description in the above depiction...
Art © AE Kimble