Celesteline's namesake originates from Saint Celestine, and was given to her by her mother, Alicira Kane. Her Canoness is Canoness Ephrala, who commands the Commandery
 
 

Alicira witnessed/partook in a battle with intervention from Saint Celestine

Pregnant at the time, saved by Celestine, decided to name her daughter after her (Celesteline)

Alicira was later injured gravely but secured by Canoness Ephrala (Celesteline's future cannoness) who was able to organize her squad to save the baby.

Despite no noble blood, Ephrala later brought her into the Schola Progenium where she was raised as a sister of battle.

Ephrala became a motherly figure to Celesteline

Eventually, Celesteline's squad was completely wiped out (save herself, she was permanently blinded), and the Inquisitors saw it as her fault. With help from Ephrala, she was cleared

Despite that, in her grief, she decided to self-invoke herself a Sister Repentia in order to redeem herself. In her eyes, every one of her sisters who fell would need to be answered in buckets of blood

Worried for her ward, Ephrala worked her magic to ensure that Celesteline would be sent to a relatively easy job

Ephrala has definitely skirted around the Code in favor of Celesteline on occasion, showing that she truly cares for her wellbeing, even if it could possibly be considered heretical. ex:

When taking the Oath of Repentance, she did not force Celesteline to shear her hair to the usual degree. Minor, but more symbolic than anything

Intervened in Celesteline's Inquisitorial trial on her behalf, based on bias (while it was indeed true that it was not her fault, this resulted in the usual interrogation to skip over usual conducts)

 
Birth
"Quick, get me someone from Hospitaller! Immediately!" Canoness Ephrana ordered.
Once the babe was extracted, the light started to fade from Alicira's eyes.
"It seems the Emperor is calling you home," the Canoness said softtly, placing her gauntleted hand on the dying woman's shoulder. The look in Ephrana's eyes was something Alicira had not seen in a long while.
"Thank you, sister. For giving her a chance."
"I am only doing my duty. Now, she will need a name, dost thy not agree?"
Alicira paused for a moment before a weak smile appeared on her face. "Celesteline."
"In honour of the Living Saint, I presume?"
"Little one wouldn't be here if she didn't show. None of us would."
"May she live up to the name, then," the Canoness returned her smile with what little she could muster. A tear, white hot, was now running down her scarred cheek. She moved her hand towards Alicira's face, brushed her matted hair out of the way, and glanced into her grey eyes. After taking them in for a moment, her gaze turned upwards, towards the char-choked sky. "Should not be a concern considering the faithful blood running through her veins!" When Ephrana matched her gaze again, she was gone.
 
Oath
"You mean to say that thy will undertake the Oath of Repentance? Does this not imply you feel... guilt over what transpired?"
"I do, yes. If only I had been more devout, more faithful! I could have done something!"
"And you believest that thy skills, everything that I and our sisters have taught thee. You believe these were not enough? You find fault in thyself, and thy faith lacking?"
"I... yes, I do believe so."
"I believe, Celeste, that you are the brightest of our order, and that the Inquisitorius have seeded doubt in your heart!"
"Thy wouldst say such a thing? You seem to reach and reach to give me protection, but soon you will overstep your bounds. Whom shall protect you when that time arrives? Not I, for I could not save my sisters when they depended on it. I do not wish to see you deposed for my sake. " She stopped to take a breath, her fingers clutching her healing ribs, "You needst not cover for me yet again, Canoness. I am no longer your ward, I am your sister. Do not forget our duty is above all. This must be the only path that I can take. I have pondered and prayed for hours upon hours."
Ephrana sighed in resignation. "So be it. Tomorrow, the rites shall be prepared. I will lead them. Forgive me, dearest sister. I have much to think about, also. I shall take my leave. Now recover, for both our sakes."