I think you'll be advised to go down the specialist watch broker route (these have been recommended here previously on other insurance threads) - or Hiscox if they will cover with your wife's business attached. Once I started on Patek, I decided to not bother insuring my >£15k pieces, I didn't think it was worth the 2% premium. I still insure my Rolex on my home insurance (generally Axa).
From reading other fora, including Patek, insurance seems to be cheaper abroad - e.g. in the US, cover can be as low as 0.5% for expensive watches. We've still to reach that level in the UK (in my experience anyway, although accept maybe they whack on a massive loading for Scottish risk!).