Coworkers daughter is Lou, is it crossing the line to use Lucy?

Not at all! Completely different! However, if it bothers you here’s a few options:

[name_f][/name_f]

[name_f]Lois[/name_f]
[name_f][/name_f][name_f]Luella[/name_f]
[name_f][/name_f][name_f]Lucia[/name_f]
[name_f][/name_f][name_f]Lola[/name_f]
[name_f][/name_f][name_f]Laila[/name_f]