I was searching the forum for wholesale infor and came across this. I'm an American in the UK, just started a business, so I may be able to help.
Is the resale ID for your benefit or for the UK lady?
If it's for her benefit, she doesn't need a resale ID #, she will be taxed regardless. If she imports your goods, she will pay duty and VAT (tax) on the value of the goods. If she is VAT registered, and will resell your goods in the UK, she can claim back the VAT paid.
The freight forwarder will require payment for duty and VAT on delivery, unless she has an account with the Customs and Excise folks.
This is how it works when I order supplies from the States, anyway, and I imagine it is the same for any goods. Have her check with the Customs/VAT people, though.
Hope that helps!
ETA I just realised you may mean the transaction goes the other way...UK to US. If so, I'm useless!