Keep the grams of carbs within reason for her evening meal, say no more than 60g and make sure the meal doesn't have a high-fat content as this can interfere with bg levels hours later.
It's best to do basal test one meal at a time, so don't worry too much about breakfast if your doing a night-time fasting basal check, but your wife's morning high may just be down to the Dawn Phenomenon which most diabetics see to some degree.
Have a read of the following which offers some good advice on basal testing, it's for pump users but the basics are much the same:
http://www.salforddiabetescare.co.uk/index2.php?nav_id=1007