What can the IRS actually do?

I have a question. An American friend of mine who has lived in the UK for more than 30 years recently learned (from me) that she was supposed to be filing taxes, even if none was owning, and also about the FBAR and FACTA reporting. Her response was to the effect of "well, I am never, ever going back to the USA, so what can the IRS actually do to me?” [She is a dual national.]

While I don’t approve of the attitude (I certainly file my taxes!), I am curious actually what the answer to this is. So, what can the IRS actually do provided there is no travel to the USA on the part of a dual national?

If she is due to inherit anything from a relative living in the U.S. the IRS could confiscate her inheritance. Also she'd need to remember that never means never with her logic - if she were to come back for just a short visit to go to a funeral or reunion (for example), or to tour the country, that could just as easily raise issues as with moving back to the U.S.

There are several things the US could do but haven't done yet. I think the greatest danger comes from UK banks. When FATCA reporting starts up this summer, UK banks will be forced to report US person account information to the IRS. Banks in Switzerland have been closing USP accounts or demanding that proof of US tax compliance be provided. That's not part of FATCA but banks would rather not have us as customers since we are trouble. It remains to be seen what UK banks will do but already the fine print for some accounts say US persons not wanted.