One reason could be for fashion. Pantyhose can add a touch of elegance to an outfit. For example, if she is going to a party or a formal event, pantyhose can make her look more sophisticated.
Comfort might be another factor. Some pantyhose are made of soft materials that feel nice on the skin. Maybe she likes the gentle compression they provide. Also, in cooler weather, pantyhose can keep her legs warm. If she is constantly on the go, running errands or taking care of the kids, the warmth and comfort of pantyhose can be appealing.
It could also be a matter of personal style and confidence. Wearing pantyhose might make her feel more put - together and confident in her appearance. It might be something she grew up seeing her own mother or other role models wear, and it has become a part of her identity as a mom. She might feel like she presents a more polished image to her family and the outside world when she has her pantyhose on.