I shouldn't be afraid to tell the birth story or tell people why she resembles a newborn at 4months old.
While you shouldn't be afraid to tell your story, you also shouldn't feel that you need to tell complete strangers. It is none of their business. If you don't feel like talking about it, don't. Just say her adjusted age and leave the rest out. I wouldn't even call it "adjusted age". You shouldn't have to relive your trauma just because someone is a stickybeak. If you want to talk about it, that is fine too. Don't feel guilty.