It is genetics, but one thing you might want to do to optimize the strength of her hair and yours is find out what the city adds to your water. Some cities add chlorine and some add a combination of chlorine and ammonia (chloramine). You could get a water filter for the house or just the shower that filters out whichever you have. If they add ammonia, the filter for that is much more expensive, so it's important to find out before buying.
Even if you have well water, consider getting a water filter for safety and to control the amount of minerals in the water. Some minerals dull hair too.