She is Annie. Somehow Ben managed to save her from the Purge because he is in love with her. Then Jeanette found her current husband David while off the island. He got her off the island right before the Purge and she left carrying Ben's child. 1962-1967 is roughly when the DHARMA children that we see in the class room are born. If those years are correct, which the most likely are, then Ben and Annie would be 18-22 if the Purge happened either December 1987 or 1988. So if could make sense that Jeanette/Annie was going to have a baby. Many older teens have children.
Charlotte was born on July 2nd 1979. That is 8 or 9 years before the Purge.
Charlotte was born in 1971 an was on the island by 1974. Annie was a child on the island at this time, so she could not be Charlotte's mother.
She is Ms. Hawking. She would be about the right age to be Charlotte's mother, and is the right nationality.
She is Olivia Goodspeed. Olivia's whereabouts are still unknown. She may have left the Island with Charlotte due to increasing attacks by the Hostiles. Horace Goodspeed stayed behind but probably intended to rejoin them later. However, the Purge happened, Horace died and the Island was lost to the outside world. As there was nothing she could do, she decided to forget about the Island, start over in England, change her name and remarry. Charlotte arrived in England at a young enough age to adopt an English accent.