If the firm is a Limited company you can pay Companies House and the Directors home addresses are listed. But if her business was a sole trader or partnership she won't appear there.

I don't think you will have any rights to reclaim off your debit card as you aren't borrowing if you use these, and the protection on Credit Cards comes thanks to a clause in The Consumer Credit Act 1988 (but it won't hurt to ask).

A major learning point for everyone here is ALWAYS to use a credit card if the cost is over £100 (the cover doesn't apply below that level), even if you pay your money into the card account before making the purchase. Whatever, just make sure you settle at the end of the month to avoid the high interest charges.