Hi Michael,
So sorry to hear about the problems your wife is having.
Some employers are becoming oversensitive about this issue.
Here is a UKBA webpage about information on the visa and about Checking your visa
I don't know just how helpful it might be. It may help.
Basically if working is not allowed it will state that.
If working is allowed nothing is stated. Can be confusing I guess.
The only number I can find that concerns advice to employers about preventing illegal working, and particularly about carrying out the document checks necessary to establish a statutory excuse against liability to pay a civil penalty is:-
Phone: 0300 123 4699
Opening Hours: Monday to Thursday 09:00 - 17:00 and Friday 09:00 to 16:30 (excluding public holidays)
The webpage is here and called Enquiries about illegal working
That's the best info I can offer just at the moment.