"Drop Dead Diva" is the story of a beautiful-but-vapid model who has a fatal car accident and is reincarnated into the body of a recently deceased attorney -- Jane (Brooke Elliott) -- who just happens to be plus size. This week, Delta Burke and Liza Minnelli guest star as two psychic sisters suing each other over their competing businesses."I've spent my life being told you are too fat, even if I weighed 110 pounds and passed out all the time, that's why this is an important show," Delta tells ET.Delta is deadly serious about weight and image, so she jumped at the opportunity to appear on the Lifetime TV series."There's so much more to a person than what you physically look like," she says. "You might detect a little bitterness there. I don't know why but at this age, at this point, I am thrilled to see [the series] and to see [Brooke] get to play it ... someone so talented."As for getting the opportunity to play Liza's sister, Delta couldn't be more thrilled, telling ET, "Well you know, I'm quite enamored of Liza."Delta recalls the first time that she saw the cabaret queen. She was presenting an award on stage and she freaked out!"And I looked down and there sat Liza Minnelli and I just went, 'Wow! Liza Minnelli's sitting out there in the audience.' I just jumped off the stage and ran down into the audience and got her autograph right then and there."As for Liza, she admits she loved dueling with Delta, saying, "I get to play a real bitch and it was heaven."The "Drop Dead Diva" episode with Delta and Liza premieres Sunday, Sept. 20 at 9 p.m. on Lifetime TV.