Copyright Paramount / CBS – Lal Star Trek The Next Generation
Lal was Data’s attempt to procreate, but rather than making a child in his own image, or more to the point in his father’s image, Data chose to create a child who could choose her own image.
A short life with a lasting impact, Lal was, for a time, thought to be the first Soong type android to have been successfully created by a person other than Dr. Noonian Soong.
Unfortunately for Data, the android who would become his daughter was in a way born with a degenerative condition that eventually lead to the failure of her neural net.
"“Thank you for my life” Lal’s final words to her father."
As a part of her death Lal experienced emotions, something Data had himself been unable to do up until that point, and would not experience for several more years, we can only imagine the impact her death had on her once his emotion chip was installed.
Data would make sure that a part of her would live on, transferring her memories and experiences to his own brain following her death, and if you pay close attention you will see his expression of her in his painting and his thoughts over the rest of the series.