Is Dr. Melfi's funny friend Jill her sister?

Dr. Melfi recalled watching Wizard of Oz with her sister when her and Kupferberg are discussing a dream she had once. Tony saw Dr. Melfi walk into a hotel lobby with a woman and say, "Jill, that's so funny" once. Jennifer and Jill both begin with the letter J. I therefore conclude that Dr. Melfi's funny friend Jill is her sister. I've said my piece.