No woman has claimed that she is the daughter of Marilyn Monroe and JFK. It is just a fiction story published by a satirical website.
This story comes via World News Daily Report (WNDR), which is a satirical website whose Legal Warning page states that the content displayed on the site is only for entertainment. No credible news reports are confirming the same. Moreover, the woman in the picture is Susan Griffiths from Tustin, California, who looks like Marilyn Monroe.
Therefore it is clear that this story about Marilyn Monroe and JFK is a hoax.