It's important to remember that roleplaying is a collaborative thing and that involves a sense of fair play. When the premise of your character is that they can only be killed by literal God or Lucifer, you're more or less declaring to other players that no matter what they do, your character is infallible and its pointless to even attempt to confront her. 

I understand trying to stay true to the lore of something, but you are playing a fictionalized version of a mythological diety, so you're not doing it a disservice to take creative liberties to make it a character that is fair in the confines of the roleplay, which I am going to assume is playing literal Gods or demigods from real life mythology. Others have made excellent suggestions how to make the character more fair, but ask yourself if you were in their shoes, would you even want to interract with Lilith? Personally, I stay far and clear of anything involving gods for roleplaying purposes because its very essence invites power playing; you're talking about entites that individually created and shaped reality in their own mythologies and now you're having them interact with one another in a medium that is centered around conflict. A lot of roleplayers treat roleplays like video games, e.g. something they need to be powerful and supposed to win, and this is part of why you're running into issues with unhappy writing partners.

Imagine playing a Lovecraftian mythos RP where someone is allowed to play Cthulhu and now you've got to figure out how to deal with an ancient and god-like entity that drives mortals to insanity just by beholding it. It doesn't work for something where players need to keep on a similar footing.

Most other roleplays involve checks and balances; let's say you're doing a generic fantasy game. One guy plays a heavily armoured knight with a sword and shield; it's understood he's not going to move silently or swiftly and be as a disadvantage to ranged attackers and magic unless he can close the gap. Another player is playing a lightly armoured rogue; she is lightly armoured, if at all, and is only carrying small weapons like daggers, poisons, and maybe a bow. It's understood that she's hard to detect and extremely lethal if she has the element of surprise, but if she's in a straight up fight, she's vulnerable to attack due to having weapons and armour that are inferior for that kind of confrontration. Another plays a mage; they are immensely powerful, but their magic has limits and they don't have the strength, stamina, or weaponry to get into a sword fight, and so on, so forth. You should never make a character that doesn't have negative attributes or obvious flaws that can be worked around by crafty players. The knight has to stop the mage but will never to get past the fireballs and lightning, so the player teams up with the rogue and now the mage is vulnerable to being ambushed from the not obvious adversary... you get the idea. 

How does that work for Gods? Some mythologies, like Norse, make it clear the Gods are mortal and can be killed. Odin is slain by Fenrir, Heimdall and Loki slay one another, Loki tricked Hodr into slaying Baldur with a weapon coated with mistletoe, Baldur's only weakness, etc. This is kind of the troubling thing about still-practiced religions; most are centered around entities people still worship and you run the risk of being disrespectful for the portrayal of these entities to someone who believes in them, as well as the issues revolving around them being beings that cannot be slain or defeated unless the absolute God deems it so. It just doesn't make a lick of sense from a roleplaying perspective. 

Honestly? It would probably be better to write a novel with a character like that because it just isn't compatible with other players unless you are willing to compromise and work to make it fair in the context of the games.