I have a character named Tiff that I like to play as sometimes. Their story was they were turned into a vampire against their will and cannot be cured (I think being able to cure what is effectively a curse to be cheap) and they are very lawful/chaotic good at different points of their story. They have dedicated themself to destroying vampires and daedra, but I'm unsure if Celestine would be able to fit into that story. Basically, I am asking if she is fully against allying with a vampire regardless of their own morals?
Short answer is, no. Keep in mind there's no way from me to check for headcanons or a particular RP that players have. She's a zealot and doesn't distinguish between bloodthirsty monsters and morally conflicted vampires.
If you really want to have her along for your playthrough, you could try that Celestine villains patch someone made on The Mod Site That Shall Not Be Named™. How you want to justify that to your character is entirely up to you, that's not my business, I'm just talking about it from a technical standpoint to stop the confrontations occurring.
Keep in mind, however, that I had nothing to do with that and don't endorse it. Any issues you'll need to speak with the author about.