Marillen was born in Valinor in Years of the Trees. From her youth, she was very curious and loves learning new things, elves says, that she has sunfire inside of her which made her want do "go on" or be active. She choose to be a healer, even people says her, that she will do not have any work. Her healing skills were described as she is able to:"iginite will to life and power of spirit" which help recover more quickly. Este discovered her talent and started to teach her. Marillen later became one of the greates healers of First age.
Her parents are unknown, but due to her red hair and character traits, there is possibility that she is related to Feanor, possibly daughter of one of his sons or his own sister. Even Calwen do not known her mother's parents as she never talked about them. When Feanor and his sons made their Oath, Marillen speak against them and after First Kinslaying in Alqualonde, she helped to heal many Teleri elves. Its unknown if she has to go or not, but when Noldor were sent to Exile, Marillen leave with them. Possibly, because she felt, that her healing skill will be needed.
After leaving Valinor, she started to live in Beleriand with Círdan's people until she met maia Lossindil and fell in love with him. Círdan asked them to lead elves into Ered Luins and build refuge there. Couple named it Edhelion and became its guardians. Later in First age they give the birth of daughter Calwen, first and last princess of Edhelion. When Edhelion was burned, couple leave Middle-earth and return into Valinor while their daughter Calwen stays in Arda.
Its unknown, when or if she met her daughter again, but due to Calwen's love for Middle-earth, there is possibility, that she will never see her daughter again.
Her name is deprived from Quenya world maril, which means pearl.
- She has unknown parents, but due to her red hair and character traits she may be relative of Feanor, possibly daughter of one of his sons or even his sister
- Marillen is one of the best healers among with Elrond and Lúthien in FA.