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.
I asked as I was sitting next to a couple in immigration last week who had not done that and were on a 60 day tourist stamp. I suspect the lady you spoke to just couldn't be bothered as your stamp clearly say Non 'o'. Just try again at that branch if you are set on that one or try a different bank.
Gov.uk provide all the information. Your main objective should be that she has a strong reason to return (job, family and property) and provide evidence.