Spoiler....
... Lichesia's mother was the Queen of Fairies. When the Church caught her, they made some experiments on her until her powers went crazy...
... To prevent her powers that went berserk, she teleported to the future, to the Black Forest where she meet Count Basillan and she lost all of her memories of being a fairy...
... They fell in love with each other and had 3 children. When she was pregnant with the fourth one (Lichesia), her memories came back, alongside the powers rampaging inside her...
.... Left with no choice, she told Count Basillan that she need to leave him and their children, concealing the truth about her powers...
... She went back to the past and gave birth to Lichesia and her powers made the forest into the Black Forest that Count Basillan was patrolling at that time...
... So technically, she is the YOUNGEST child, but OLDEST by timeline

what if she was born at the wrong time? which is why she's older than her brothers? What if her mother's powers is weakening so as the queen she needed someone to pass it through which is why she was born prior to her timeline and she can't go back to her adult form because her date in which she should be born has only recently just corrected and she turns back with the fairy queens crown because it resonates with the power she has accumulated at that age?