she is a skilled dragoon and gunbreaker with a strong desire to keep her friends safe even if it would cost her own life or happiness. that said, she is anything but selfless--she has little regard for their own desires when it comes to self-sacrifice.
Although Lehna would tell anyone that she grew up in Old Sharlayan, what is less known is that she actually grew up in Sharlayan--the colony in Dravania--until it was fled.
Lehna ran away from home as the colony was being evacuated, wishing to stay close to the dragons and Coerthas, as her dream was always to become a dragoon. She was found by a gruff man named Zach who attempted to find her mother's Keeper of the Moon clan, not knowing that it was actually a cult of miqo'te who detested Menphina and a cult that thought Lehna, with her Echo, was the perfect candidate to channel their divinity. Zach kidnapped Lehna before the ritual was completed, but this completely broke any potential relationship Lehna could have had with her mother.
After a year or so, Zach realized that Lehna's father was in Old Sharlayan and had been frantically looking for her. Despite Lehna's insistence that she did not want to go there, Zach determined it was safer than having a child tag along with his mercenary work and tricked her into returning home. Though Lehna was resentful, she was grateful when her father agreed to keep Zach as Lehna's trainer. Zach taught her everything he knew about combat and although he was a viper and not a dragoon, he did everything he could to teach Lehna how to properly wield a lance.
Eventually as Lehna grew, her resentment for her father grew more and more. Her father thought education was of utmost importance, but Lehna was dyslexic and, unfortunately, neither of them were able to work that out in order to help Lehna have an easier time learning.
Zach eventually left to assist in a great Calamity that was occurring as the moon Dalamud began approaching the planet. Zach never returned and was presumed dead. Lehna refused to accept this and, at age 21, decided to go to Eorzea and chase after Zach and start her own adventures.
This is where the traditional timeline of FFXIV's canon begins, and Lehna follows it mostly the same. A skilled lancer, it did not take long for Alberic to request her help in chasing down a rogue dragoon. This eventually led to her becoming the Azure Dragoon, one of the leaders in the city of Ishgard's centuries-long war with the dragons.
During the era of Shadowbringers, Lehna found herself struggling with the ability to maintain a connection with the aether provided by Nidhogg's eye (now gone completely except for the remaining tendrils tied to her and Estinien) due to light corruption. She picked up gunbreaker instead, hoping the excess of light-aspected aether would assist her in protecting her friends with Hydaelyn's blessing.