Sharon Tate
While they referred to her only as "Sharon", she was married to Roman Polanski and went to see a movie starring Sharon Tate and acted out the parts, I am going to go out on a limb and say the part my Margo Robie was indeed Sharon Tate.
I certainly remember the name and looking up on the web it says Sharon Tate was murdered Aug 9, 1969, and that is the date they showed as they were on the plane. We all, or anyone my age, knew she was murdered by Charles Manson. There were those hippies from the ranch that came and broke into Rick Dalton's home. While often referred to the man as "Tex" they did mention a Charlie once. And they referred to another as Squeaky. So can we assume the people that broke in were Charles Manson and his gang? And they killed Sharon Tate, so Charles must have survived in Rick's House, and gone into Sharon's house and killed her after Rick had gone home again after having his drink? The movie ended before that happened.