Frederica sees Shinei as an older brother and substitute for Kiri. She grows an attachment to him similar to that with her knight. Due to her regrets with Kiri, she frequently whishes to be at Shinei's side, even when he would rather not. Her view of him would later evolve from being Kiri's substitute to a separate person that was still her older brother. She is one of, if not the only person to call him Shinei instead of Shin.
Upon initially meeting Lena, Frederica regards her with dislike and caution. This stems both from her aversion to the Republic's Alba that stems from their persecution of the Eighty-Six, as well as some sibling envy that stems from her being aware of Shin's feelings for her (not unlike Kurena). However, as time goes on Frederica develops more respect for Lena and goes on to serve as one of her control aides in the Vanadis, using her psychometry power to observe the Eighty-Six during battles. Much as she does with everyone else, she refers to Lena by her full name, Vladilena.
Kiri was Frederica's personal knight. She seemed to rely heavily upon him as an older brother figure, as well as her caretaker. Her attachment to him became a burden once Kiriya was assimilated by the Legion into the railgun-type Morpho. She believed she was the person who created the monster he became. Frederica was able to let go of her lingering feelings and regrets towards him come the Morpho's elimination by the Nordlicht Squadron.