Good evening and thank you very much for your question.
The engine management unit (ECU) has detected a fault and this is why the engine malfunction warning has activated.
A fault code should be stored in the ecu's memory which will point your garage in the direction of the fault. The only way to find out what has caused the problem is to take your car to a garage that has the correct diagnostic equipment, and have a diagnostic check carried out, which will reveal what the fault code is.
Most garages have this equipment nowadays, so I would suggest phoning round for a quote unless you have a garage that you use regularly. You do not have to go to a main dealer for this test.
There are many reasons why the light could come on, so guessing would not be wise and will almost certainly end up costing you money.
Your car will be safe for your wife to drive, unless it has a misfire. If it does have a misfire, the engine will be under powered and you will fell a juddering sensation. This will cause unburnt fuel to enter the catalytic converter, which will seriously damage it. Providing there is no misfire, then you will be ok, but I would suggest that you have a diagnostic check carried out as soon as it is practical for you.
I hope this answers your question.