Not sure which thread you're speaking of but  looking on her product page at RDNA, there's no mention of a rib cage morph or anything that could be similar. I guess it could be included but not mentioned on the page - you have her, you could check that. She's got a lot of morphs though and Tate did a great job with her. I'm sure if you ask, Tate may even be able to do a rib cage morph as part of an add-on for My Michelle.