Strange compliment

I was seated on a park bench, when an old lady who came and sat next to me, smiled and said, "You are very pretty."

I must have had a disbelieving expression on my face, because she was quick to assure me that she had given a sincere compliment.

I tried to explain to her by saying, "It's just that I hardly ever get to hear pleasant comments about my looks."

The old lady smiled and said,  "Just because you are plump does not mean you aren't pretty."