I think all relationships are one sided one time or another or lots. If a man does hard labor all day then comes home he is going to fall asleep at the dinner table. If the wife was wanting "it" all day then here he is asleep it's going to get tiresome for her.
It follows the same with her. She was doing way too much and falling in bed snoring. She is too tired. They need to plan some one on one time each week.
BTW, moms and dads. When the kids grow up and go off to college it's just going to be the 2 of you. What will you talk about? What will you do with your evenings? What interests do you share?
Sex isn't everything but to get to it there must be some intimacy in the relationship. Go swing on the playground, splash around in the sprinkler when it's watering the grass, play together, watch a movie snuggled on the couch, do stuff together then sex will come easier.