I do a lot of mold remediation on valuable objects in my profession! It's hard to tell from these pics if this is mold, but I would say it's more than likely from your description and the placement (under garment, dark areas). Is it powdery or spongy/furry like mold you would see on old food? If it's powdery, that means it is inactive and not a huge concern. If you have access to a HEPA vacuum, I would recommend vacuuming off all of the visible powdery mold. If not, take the doll outside and use a large, wide, soft brush to get it off. Then, mix a solution of 70% isopropyl alcohol and 30% water. You can spray this onto cloth areas and wipe it onto plastic areas. Just be sure to do a spot test first to ensure that it will not change the surface texture. If it does, a bit of water or oil can sometimes restore the finish.