...a simple examination by a doctor can tell if the child's been molested or not. If not, great. Children touching themselves and other children is normal, but the obsessiveness you describe is not normal behavior...even you realize this or you wouldn't be writing.
Often molested children develop vaginal infections that itch, hence actions that seems like self-gratification.
But this is too important to hide your head in the sand in the face of such huge red flags! Set your mind at ease and be SURE nothing untoward has happened to your little baby girl before pronouncing her attempts to get you (and maybe others!) to spank the monkey her as innocent. Can you imagine her placing her little friends' or adults' hands on her vagina? She'll do it with others if she did it with you. Through no fault of her own, she'll get quite a rep at 4, with no parents allowing their children to play with her.