You don't, cook them for the same amount of time that is. Once you have the grill heated you will want to start your wife's steak first and once you have flipped hers (for a one inch steak after about 8 minutes) place yours on the grill. After 4 minutes flip yours and wait another 4 minutes then remove both to a platter to rest 1-2 minutes prior to serving. Your wife's steak will be done at the same time yours is and you will both have perfect steaks. Remember the key to keeping your steaks from drying out or getting tough - flip only once.
Here is a chart to help with timing on different doneness based on thickness:
Thickness
Rare
Medium
Well
Heat
1"
8-10
12-14
16-20
High
1 1/2"
10-14
16-20
22-26
High
2
12-16
18-22
24-28
Medium
