The people in the organization actually knew about the fake mission or at least the people who was on Wisteria and Hue's side as the coincidence of her grandparents finding her and Reen's so called safety guarding was too coincidental.
As they did not want to expose this they tactfully agreed not to say anything especially in this kind of organization wherein people would use all their means to get what they want even using riot and assassinate (if they have the skill) the current head.
Because of this reasoning, they had to pretend that they did not know anything thus despite their reluctance of her parting even just for a year they tactfully all agreed for her to train on the branch site.
Mirly knowing the scheme of Hue and Wisteria was yet again full of gratefulness at the couple. She was also having troubles at her school which she had accidentally told them that added to the reasoning for her punishment to be transferred to the other branch.
They were not only giving her a way to think about what she was going to do from now on if she was to stay still while currently bringing the burden of her mistake [1] or to let go and leave the organization and live a peaceful life with her grandparents.
When Reen found out that Mirly was leaving she was very sad which seeing this made Hue and Wisteria question their so called punishment to Mirly [2]. Seeing the obvious distress of their god child and soon to be daughter made their heart ache. But knowing that it was for Mirly's future's growth they steeled their hearts and did not changed their decision.
Her decision will eventually be relieved when she returns from her 1 year exile.
...
Hue and Wisteria having their heart frightened badly at what happened to Reen's family had revealed their hidden identity to Reen to make her trust them more.
Regardless of her decision to stay or leave they would still silently protect her.
Reen had a similar reaction with Elena which warmed the couples' heart. Reen believe in what Hue and Wisteria showed her throughout the days they spent with each other.
She believed like Elena that they wouldn't aimlessly kill anybody without proper reason.
After her acceptance and a few days past after she agreed to be their adopted daughter, they had encourage and half forced her to learn self-defense also training her in using a gun and a knife.
Reen contrary to their expectations was excited knowing that they would teach her but soon regretted her decision when the Spartan training begun.
She repeatedly wanted to quit but after each day went by she actually realize that what happened through that day was fun and was not as bad as she thought it would be. This roller coaster emotion happened throughout her training until she finally wholeheartedly accepted the training without complains.
Author's Notes:
ξ(✿ ❛‿❛)
FYI: The emojis are not mine, got them from Google
[1] Mirly despite eventually realizing that the mission was fake, she still wholeheartedly tried to accomplish it.
[2] See Chapter 92 for the full story