Lal was a Soong-type android constructed by Data using his own construction and programming as a model. She suffered a cascade failure in her positronic brain shortly after her construction and died.
Lal had essentially the same physical and mental abilities as Data, with minor exceptions. Unlike Data, she used verbal contractions in her speech without difficulty, a behavior that was apparently blocked in Data's programming. She also began to exhibit emotions before dying, a feat that Data would not accomplish until he received an "emotion chip" from Doctor Soong.
When Starfleet learned that Data had constructed Lal, they sought to seize custody of her. Since a Starfleet court had already ruled that androids like Data were sentient beings who could not be considered property, Admiral Haftell attempted to take custody of her on the grounds that Data was not a suitable guardian for her. Captain Picard opposed Haftell's decision, but no final ruling from Starfleet or the Federation was received, since the stress of the situation caused Lal's positronic brain to fail before the issue ever went before a court.