gone from heavy to bombshell

EMOTIONAL FIRST AIDを読んでいると、知っている単語ですが、おやっと？と思う表現が出てきました。
Serena, the high school teacher who had gone from heavy to bombshell, was also quick to judge others and their intentions toward her. She was certain any man who expressd an interest in her did so solely because of her appearance and had no intention of getting to know the "real" her.
"bombshell" は "dynamite" を連想し、セクシーな容貌の女性を連想しますが、"heavy" は単に重い、すなわち太った人を連想します。 "gone from heavy to bombshell" で、ただのデブがカッコ良いセクシーな容貌になったと解釈するのは文脈から何か変な気がします。まず "bombshell" の意味を確認します。
・Oxford English Dictionary: informal A very attractive woman.: a twenty-year-old blonde bombshell: Rhos of course, wore only black, being the blonde bombshell she was.
・Collins Dictionary: an attractive girl or woman (esp in the phrase blonde bombshell)
これは予想通りですね。さて、問題は "heavy" です。
・Collins Dictionary: If you describe a person's face as heavy, you mean that it looks sad, tired, or unfriendly.: Many of them were policemen, with their heavy faces and cropped hair.
・Merriam-Webster's Online Dictionary: lacking sparkle or vivacity, lacking mirth or gaiety
"heavy" は重い、がっしりした、重大な、大変な、きついなどから上のようなかなりニュアンスの異なる意味もあるのですね。
引用文の　"heavy" はデブと解釈するより、"lacking sparkle or vivacity" の様な意味が合っているようです。