only silly guys in here

When she was very young, nothing bothered her much as she was just a wild baby exploring the world x) And Shade was a good father figure to her. However, as she grew older, she realized that she doesn't really "fit in": yeah, Pandora is a crazy planet, but not every person there is crazy. There are plenty of "regular folk" like Shade or other people from their town - and many others. And she was frequently called a monster, a mutant and many other things by the regular kids and even adults. She was wild though, could bite them or fight with them in a pretty feral manner, and, even though she protected herself, it didn't help the situation much. She wasn't crazy enough (and too small) to fit in with the psychos or bandits, was "too human" for actual monsters living on Pandora, and for a long time she had no idea she was a Siren, as even for Sirens she looked too different. Only when she hit her teens, she was able to confirm that she is one, started using her powers, and in her human form she could see the full extension of the glowing pattern she had on her skin. She still, however, didn't know why she wasn't born "normal", and there were no older Sirens around.

At some point, she decided to become independent and live on her own. Her "wild" upbringing was helping that a lot, and she felt fine being away from people. She'd still visit Shade frequently, of course, and at some point she'd even met Zer0 and could hang out with him for some time. As Zer0 is a mystery himself, they had some common ground between them (though constantly listening to his haiku were exhausting xD). Sadly, Vault Hunters attract attention, not always positive, and that was the reason why she got spotted by a big bandit gang (could be the beginning of Vallory's gang, but before she took over). And local scientists like Tannis already declared that there may be some connection between Sirens and the Vaults. And they noticed that she's a Siren, but also pretty young (and dumb). After the first Vault on Pandora was opened, there was plenty of weird and valuable stuff around, but it wasn't so easy to get it when you're just regular bandits. And when Eridians, the aliens that are guarding the Vault, are everywhere. The Sirens like Lilith were too strong for them, and hiring a Vault Hunter is expensive, so they decided to wriggle into her favor and use her to gain access to the area. She didn't know she was dealing with bandits first, she naively thought it's a rare case of nice fellows just wanting to be friends and such, plus the Vault could have answers about her origin, and the new "friends" confirmed it.

At some point, she realized she was being used, and got into a fight with the bandits - and lost, as there were too many of them, and she had too little experience, and they knew about Shade. She got kidnapped and told that she'd do everything they told her to do, or they'd kill Shade, so she had to obey. She helped them to fight the way to the Vault and get some of the riches, and during the process she felt that she really does have a connection with Eridians - they boosted her powers and helped her to get free, and kill every presenting member of the gang. She was worried about Shade though, so she left immediately to find him before the remaining members found out what happened and could harm him. But she was too late - the water source in their town of Oasis was poisoned, and every single person there died. Except Shade though - he lasted longer, but dehydration made him insane, and he turned corpses into the stuffed dummies he could talk to (though she didn't have much of a problem with this part). As she was gone for at least several months, he didn't believe she's real, and she had to adapt to the new reality.

She never got back to the Vault after that as she felt it was a source of more trouble than anything good (in her view, the price was too much for a bunch of physical stuff).

That lasted for years, and became a bit easier as her powers, enhanced by the Eridians, wasn't only serving the destruction,  but could eventually "heal" some part of Shade's mind, so the moments of clarity became more frequent (she didn't know it's the reason, though). And you still need money, whether you like it or not, so, when Shade decided to use his World of Curiosities as a spot of illegal deals and smuggling, she didn't resist, but would watch over him in the shadows in case something goes wrong.