Change in Tessa
Jem and Tessa were in Los Angeles in August 2012 when they found out that Tessa was pregnant with their first child. Tessa started having difficulty with her ability to Change. When Tessa Changed into Rosemary and was mortally stabbed by Fal, Tessa was unable to Change back into her original form completely because of the child, unwittingly saving her from the wound. The child's presence in her body, however, prevented her from Changing back for days before Tessa finally managed.
Brother Enoch informed her of her pregnancy, and Tessa later told Jem, and though Tessa dreaded the thought of watching Jem and their child age and die before her, both parents happily looked forward to the child.
Moments before her birth in March 2013, the ghost of Livvy Blackthorn arrived in the conservatory of their home while Tessa was in labor. Livia, in her disassociated state, briefly considered switching places with Mina. Magnus Bane later arrived, sent Livvy away, and helped Jem deliver the baby.
Jem and Tessa named her after Will and Rosemary and gave her both of Jem's family names. She was cherished by her parents and their friends, and she was raised alongside Kit Herondale, whom her parents took in months before her birth.
Mina has black hair and dark eyes. According to Magnus, she has Jem's slender fingers and Tessa's chin.
Mina's first name Wilhelmina was given to honor her parent's beloved Will Herondale. It also refers to "wild rose," for those whom Jem loved that "best grew in beautiful rebellion." Jem also wanted to give her a Chinese name, and they went with "Yiqiang" for "remembrance" to commemorate Rosemary and Jem's Silent Brother name Zachariah which meant "remember."
- Through Blood, Through Fire (first mention)
- Queen of Air and Darkness (mentioned only)
- The Lost World (mentioned only)
- Forever Fallen (first appearance)
- Her parents also considered giving her Tessa's maiden surname Gray but eventually decided against it, with Tessa wanting Mina to decide her warlock name herself if she chose to be a warlock.
- The author Cindy Pon helped Cassandra Clare come up with the child's Chinese name.
- Mina's favorite flavor of ice cream is vanilla.
- According to Jem, she talks in her sleep like Tessa. 
- ↑ Through Blood, Through Fire
- ↑ The Lost World
- ↑ 3.0 3.1 3.2 3.3 Forever Fallen
- ↑ "Cindy Pon has even been so kind as to help me with Chinese baby names..." Cassandra Clare on Tumblr
- ↑ Tales from the Shadowhunter Academy launch event | TMI Source video on Facebook
- ↑ Shadowhunter Army August 2019 Newsletter – Shadowhunters.com