The CRB in itself doesn't come back 'ok' or 'not ok', it simply details somebody's criminal record and it is up to the potential employer if they think something on the record means the person can or cannot work for them.
As your friend went to court this offence will show up on the check but I would think it very odd if the nursery thinks a motoring offence means they are not suitable to work with children.
As a precaution I would get her to tell them first (in very simple terms) before the check comes back so it isn't a surprise.