(Sorry for the late reply; I was on mobile when I first got this in my inbox and wanted to answer it on my laptop so I can type easier)
Okay!! I actually have quite a few headcanons about Lucy. I see her as being really quirky ever since she was a kid. She was totally into action and spy movies, such as James Bond movies, and she always preferred acting out badass scenarios with her dolls instead of the stereotypical girly types. She wasn’t popular in school, but wasn’t necessarily disliked. Most people saw her as too “weird” and energetic, but she didn’t mind because she’d always been confident in who she is. She was also probably really into martial arts, considering her quick self-defenses in DM2. From an early age, she knew she wanted to do good in the world, so she combined that desire with her love of badass spy stuff, leading to her ending up working for the Anti-Villain League.