Better to redact a bit and have the thing that she was made a vessel for be another dark entity that I make up from scratch.
This might be best. For myself, I have always tried to use pseudonyms for the Crawling Chaos in relation to my character's lore, just so I'm not obviously namedropping that there might be a Mythos connection (probably to avoid some of the same problems you've been encountering - preconceptions and easy associations that might not apply to your PC's lore). CoX has some possible in-game lore connections you could use, particularly the Circle of Thorns (http://wiki.cohtitan.com/wiki/Circle_of_Thorns), the Banished Pantheon (http://wiki.cohtitan.com/wiki/Banished_Pantheon), the Servants of Rularuu (http://wiki.cohtitan.com/wiki/Rularuu_the_Ravager) or even the Coralax (http://wiki.cohtitan.com/wiki/Coralax).
I especially dread the fireworks...
Say no more, I was beginning to think this already before you logged off last night. I consider the guy a good RP'er and a good resource for coordinating mythos elements in a RP storyline, but I won't suggest that he knows more or better than anyone else. You two might not mesh, I couldn't say because I don't have the sensitivity to these issues that you have to know where the pitfalls and bones of contention will lay.
Re: Being one of the five...
This might be best. For myself, I have always tried to use pseudonyms for the Crawling Chaos in relation to my character's lore, just so I'm not obviously namedropping that there might be a Mythos connection (probably to avoid some of the same problems you've been encountering - preconceptions and easy associations that might not apply to your PC's lore). CoX has some possible in-game lore connections you could use, particularly the Circle of Thorns (http://wiki.cohtitan.com/wiki/Circle_of_Thorns), the Banished Pantheon (http://wiki.cohtitan.com/wiki/Banished_Pantheon), the Servants of Rularuu (http://wiki.cohtitan.com/wiki/Rularuu_the_Ravager) or even the Coralax (http://wiki.cohtitan.com/wiki/Coralax).
I especially dread the fireworks...
Say no more, I was beginning to think this already before you logged off last night. I consider the guy a good RP'er and a good resource for coordinating mythos elements in a RP storyline, but I won't suggest that he knows more or better than anyone else. You two might not mesh, I couldn't say because I don't have the sensitivity to these issues that you have to know where the pitfalls and bones of contention will lay.