There seems to be at least one lie in Jacqueline’s story: she claims Simon doesn’t like bossy women—but arguably, Jacqueline herself is bossy, given that she took over his whole plot against Linnet in order to plan it better. This is the best evidence that she might be fooling Poirot. Then again, the narration specifically indicates that Poirot has no doubt about Jacqueline’s motives—and Poirot is usually right, particularly given how he just outsmarted Jacqueline.