Charlene was the holographic wife the Doctor created to explore family life, first perfect and later more realistic.
Charlene was part of a holographic family the Doctor programmed on the holodeck to learn what it meant to be human. In its original form the family was flawless, with a devoted, cheerful wife and two well-behaved children.
In Real Life, B'Elanna Torres found the program unrealistic and rewrote it, making Charlene a busy woman with her own job and less time for her family. The Doctor struggled with the arguments and pressures of the new program, and the family's crisis over their daughter's accident tested him in ways he had not expected.