Deliberate mistake: When Jack fights the impostor, they are roughly the same height, but when the impostor is revealed to be Angelica, she is suddenly much shorter than him. (00:21:30 - 00:23:50)
Revealing mistake: When Jack Sparrow is chased in London, being on the carriage and looking back to his chasers, you can see the broad tire tracks of a modern vehicle in the mud. (00:16:55)
Continuity mistake: When the movie ends, Barbossa is given his hat with no feather. A frame later the feather appears. (02:04:55)
Chosen answer: She most likely went to stop the ritual, she probably didn't want her tear to be used by the likes of Blackbeard. She knew that Jack would use it wisely.