Try this, greybeard, it might seem like you're going round the houses, but it might work. I don't use Visat but I assume it handles CSV files.
Create a new Identity in your OE for your friend, that should give you a clean Address book in that new Identity. Then Import her backed up wab file to that new identity. Check the Address book in that Identity to see if it has been imported. Then Export it to a CSV and see if Vista will accept that CSV file.