She didn't kill him directly, but she did cause his death. However, it was not by using voodoo. It was because she hinted to Mr. Mereaux about his wife's and her father's affair.
The reasons why Eve's "voodoo" was not the cause of Louis's death?
1. When Roz has her fortune told by Elzora, Elzora says that, "Sometimes a soldier falls on his own sword," insinuating that she already knew about Louis' impending death.
2. When Eve asks Mozelle how to kill someone with voodoo, she angrily answers, "You can't kill people with voodoo! That's ridiculous!" Considering how easily she fooled Madame Renard into accepting her fake "protective charm" earlier in the film, Mozelle would obviously know if it were truly possible to kill someone with voodoo.
3. Consider Elzora's hatred of Mozelle. When Eve propositions her, she is surprised, not only by the amount of money she has, but her boldness as well. Also, when Eve tells Elzora that Mozelle is her aunt, her eyes light up, and she continues to smile throughout the conversation. Because she is psychic, Elzora already knows who Eve intends to "kill." Add the fact that Elzora also already knows that Louis is going to die, and you have a clear opportunity for Elzora to not only profit off of Eve, but get revenge on Mozelle by causing psychological trauma to her own neice. Therefore, it's possible that Elzora lied about the "wax coffin" so that Eve would blame herself as the direct cause of her father's death.