For decades the UK has been selling licences to launder money through the country's institutions and tax free at that, to the irritation of other authorities including the EU. You buy yourself "Non-Domiciled status" while still living in the country and shove through as many billions as you like - people from all points of the globe have been doing and continue to do this, the London financial centre is to a degree built on it.
The cost of the licence is perhaps £35000 and I suspect this will not suit your friend because of the relatively small sum she has hidden away. I believe that if it comes to a question and answers session with the taxman then she will be regarded guilty unless she can prove her innocence even though in the scheme of things her sum is a pittance, and however likely it is that she is innocent of any and all wrongdoing. The tax authorities are arguably the most potent force in the land and have forced lawyers, bankers, employers, etc. to do the policing and collecting for them.