they don't ask for proof they ask where you work and your monthly income as here the male has to provide for his family. I'm not sure what you would do if not working.
immigration will check you are working and can support your family (ask how much you earn each month) but there is no set amount needed and they don't ask for proof.
Immigration have said it is not real, not sure what you want to check as it is up to them the allow or deny entry. They have said it is fake and she can't enter, as others said if she applied through the correct channels and been approved then she would have been issued a real visa and would have be allowed to enter.
technically you have never had to convert to a non B to get a work permit when you are on a non O due to marriage, a lot of places that employ people prefer it and will say they have to (even asking immigration to state the same) so that your visa is tied to their company.
According to the visa information you have to do a yearly check with immigration to ensure you continue to meet all the requirements (insurance and money) and you should still do the 90 day report.