Fact is that we do NOT KNOW her history. She could have been in NXIVM which has been going for some 20 years or so.
And we don't know for sure that the tattoo covers up an NVIVM brand. It could cover up something else, maybe a scar.
Right now there is only a guess. Yes, it is a reasonably educated guess given the source material available, but it is not enough. There is only enough there to ask Stormy the question publicly. She may or may not answer.
And there is enough info to inform the FBI field office that is investigating NXIVM. If they believe this to be a lead, they can and will investigate further. But that means HANDING IT OVER to them. They may say nothing publicly for years for very good reasons. And I say years because NXIVM has tentacles that reach out and will take years to unravel through the court system. Many people were involved in crimes.