Often, staying in a cramped up position, or sedentary for a prolonged period can cause muscle cramps and poor circulation. Tips from Quantas. Check this site.
Make sure she’s getting adequate water & electrolytes as deficiencies in either can exacerbate cramps. Have her try changing her leg position often, in case it’s related to circulation. I’d also try incorporating some myofascial release techniques for the hips, glutes, hams, calves & feet into her workout routine. Sometimes those recurring knots aren’t released by just stretching, so the self-massage can be beneficial. You can give her seated calf/hamstring stretches to practice so she’d be able to do them sitting in a car (ie. extend the leg long & pull the toes up off the floor, leaning forward slightly from the hip). Make sure she’s got similar mobility on the left and right sides of her body. Finally, I’d strengthen those calves, hamstrings & glutes! If they’re not easily overloaded they’ll handle longer times on the road. Good luck!
Sara, I agree with you, that myofascial release techniques would probably be the best way to help alleviate this problem, along with increased water consumption. I would suggest that she use a foam roller prior to going on a longer road trip. I sometimes have leg cramps and will use a tennis ball if I don’t have a foam roller available.