The thing is, her goods costs are about %40- 50 of her turnover, and most of the goods don’t have VAT on them: she does aesthetic treatments; botox and dermal fillers - both prescription medicines so VAT exempt.
In which case, it may be reasonable to split her charges - charge for the goods at cost (and exempt from VAT) and then the rest for the service element (VATable) and this doesn't look like (because it isn't) artificial for tax purposes, and then the amount of potentially VATable supply she makes will be 50=60% lower than total turnover and then should be well under the threshold? The key thing here is that VAT threshold is not based on total turnover, it's based on VAT taxable turnover, so any exempt supply (i.e. the sale of exempt prescription medicine) won't count towards the calculation.
I am an accountant, but not a tax specialist, so worth checking with someone who actually works in the field that I'm not talking rubbish. There might be a question that arises around that split - I suppose the answer might be determined by whether your wife would be able to sell the goods only, without the service element. If she could, then I think it would be okay.
Oh, hang on a minute, I've just read the bit about being a registered healthcare professional and being able to sell the service as (zero rated) medical treatment - if that is the case then I can't see what the problem is - you may have to register if your taxable supply is above the threshold, but since it's zero rated there's no impact on what you need to charge to customers since the VAT you will be adding on ranges between zero and zero. So just register and start charging your customers VAT, at the relevant rate...
You'll have some additional paperwork for the VAT return, but most of the numbers on it will be zeros so something that shouldn't be overly onerous. You may even (check this one with a tax specialist as well) gain since you will be making taxable supplies (albeit the tax is at the rate of 0%) so could possibly look at recovering some input tax?
And just to add to others' posts - frankconway is talking utter rubbish, sole traders do not have any interactions with Companies House (there's a big clue in the name, Frank). If the business is growing you might want to consider the potential advantages of other structures, but that's a completely separate matter and one that you should also take specialist advice on.