Multiple realities(covers information from several alternate timelines)
Louise Nielsen was a Starfleet officer in the 24th century
In 2353, she was listed as a Starfleet Operational Support Services officer on a directory placard at Starbase 32, Maxia sector. Her office was located in room #45245. (TNG: "Violations", directory)
In an unknown, alternate future timeframe, she was listed as an Engineering Division officer on the dedication plaque of the USS Pasteur. (TNG: "All Good Things..." dedication plaque)
This character was only mentioned in writing.