She was once the baby to a powerful and rich couple, who was deemed the next heir to the fortune. However, a close (former) friend of the couple was angry that the baby was going to be next in line and, being greedy and wanted it for themselves, had her parents killed when she was just a baby (She was also going to be killed, but her parents got her to safety before they died). She was later found and taken to an orphanage.
Lost Legacy is not her birth name (she never found out what her real name is/was), as it was a name given by herself, upon learning that a legacy has been lost with her being separated from her parents. (She doesn't know her full past)
As for how she is today as an adult, Lost Legacy is doing pretty well. She found out that she had a talent for singing and music, and so she has had a successful career as a punk/rock. She can be kinda moody and a bit down at times, but for the most part, she is a nice and kind pony. She also has a good ability over ice and crystal related magic and spells too.
She is still wishing to know more about her parents and her past, and wants to get to the bottom of this some day.