I have been having this issue as well, she disappears at different points in the fight for me, always when she jumps and then she does not display. She shows up on hate list still but I am unable to target her. Many times after she jumps again she will then re-appear on the screen and I can target her again.

This happened with several different party setups over the course of 4-5 hour of trying last night and has happened to me several times previously. While it suxs to see I am not the only one experiencing this issue I am very hopefull there will be a fix for it.