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You are more than welcome. I know of someone who accidentally tried to claim TVA back on an invoice that they had paid but they got in trouble by the TVA authorities because the person who raised the invoice wasn't registered for TVA. It was a genuine accident in the book-keeping but the authorities were not impressed. I can understand that you want to help your friend but it is probably not a good idea to help in this way as it could lead to all sorts of problems. It is probably not a good idea to even give a invoice that is dated after the business closed because it is easy to check a SIRET number online. I hope her business goes well though, as we all know its not easy to run a business in France!
Putting your husbands SIRET number wont make any difference as your friend will not be able to claim the TVA back on any invoice that you produce because this is not a TVA number. In order to produce a TVA invoice you will need to have a TVA number which is different to your SIRET number. As your husband was an AE he does not have one and any previous invoices that he raised should have stated that TVA is not applicable with this statement 'TVA non applicable, article 293 B du CGI'.