Contrary to common belief, horses are not allowed on most WMAs that are state owned. While the information in post 4 is correct, there are very few WMAs where that information applies, most are posted no horses, bicycles or ATVs allowed. Many WMAs on federal land also are not open to horses. Have your mom make a few phone calls to find out where she may ride and what conditions apply. Look in the front of the regulation booklet for the region office of the area she is interested in and ask them, if it is federal land, there are a lot of phone numbers for the federal ranger districts listed in the back of the regulations to get that information.
A man, like a river that follows the course of least resistance, is likely to end up crooked.