My 13 year old daughter just showed me that the bottom of her rib cage is not symmetrical. It seems that in the lower portion of both sides, the ribs are curving inward a bit more than what is normal and on one side the exaggerated inward curve starts about one rib higher than the other side. I don t know if this is a change in her rib cage or something we have never noticed before. Her dad has a rib cage deformity on one side, closer to his mid-chest that is nothing like this (his is more of a protrusion) and was told it was from years of breathing difficulties from childhood asthma. I can t imagine they are related, but I thought I d provide the info anyway.
You are correct in assuming that the condition in the father and in the daughter are probably unrelated. What your daughter has, to use jargon, is rectus excavated - or, in English, an excavated chest. This is probably present since birth, and has got exaggerated now that she is growing fast. You shouldn't worry about it, as it is just a minor disfigurement, and will not affect her in any functional way. Regards.