Literally, NOTHING would happen. Yes her reputation might take a very small hit, but it's nothing that can't be explained away with being vulnerable, influenced, in a bad place, never did it around my kids etc. The police would not give a flying duck about someone taking a bit of sniff years ago. Personal drug use doesn't get disclosed for the purpose of a DBS check and it is wholly irrelevant in most cases, even historic dealing is not disclosed! She would have nothing to worry about at all and I'd actually I'd respect her for speaking out, admitting she made a mistake etc+