I feel Lakshmi's voice fits her because it alludes to her true nature. The whole loving motherly quality is actually an allusion. Lakshmi's true personality is actually quite sinister, and in a way she is worse than Sophia in promising false "bliss". Think of it like a Genie who twists the words of your wish into their own desire, so that you reap the folly. She knows she is manipulating you and when you don't fall for her tricks her true colors show.
