I don't have an opinion on whether Elaine is Jewish, but people are making logical jumps that are not valid.
Just because someone says they are not XXXXX does not automatically mean that they are not XXXXX.
"There's a singles club dinner for homosexuals tonight; do you want to attend?"
"But I'm not homosexual." "Me neither."
Either of these parties could be homosexual but not be admitting it. So, though Elaine says she is not Jewish, she actually could be. She could be a non-practicing Jew that considers herself not Jewish because of her non-practice. However, one can convert to Judaism, but if one is born Jewish, one will forever be Jewish, regardless of any theological decisions one may make in one's life. Even if a Jew converted to Buddhism, that person is still a Jew. Being Jewish is more than the religion; it is being of a separate race/ethnicity.