you should probably get rid of the doll until you learn a little bit more of how these things work. a thrift store can be a place to find "haunted" objects, but not necessarily as you are thinking. not always actual ghosts or spirits. everything holds some of the energy and essence of its former owners or those it has came into contact with. everything has a story to tell. some of that energy may be good, happy, from better times and some may be sad, unhappy energies... some may bring depression or uneasy feelings if you can feel it. so its not just the dangers involved, its also learning how to tell the difference and how to accept or block the energy it may hold......
Duke is right on the EMF topic. the phone apps are pretty much useless, unless youre looking for a router or computer in the room....lol.... and also on the "expert" part. dont let just anyone convince you they are an expert or "in the know" when it comes to this... read around some of the threads and learn what you can. how to close out an investigation as well as how to prepare beforehand. ask questions, participate start fresh with a new look on all this.... good luck and welcome to the forums