This^^^I use SPARCO "Tide" gloves (see link) Sparco USA- they have little tiny rubber "volcanos" on the palms and fingers that help grip the steering wheel. They are spendy....but they work very well.
Other options I have done in the past.....scuff up the suede on the steering wheel as much as possible before each time on the track. Also, I have actually used skinny strips of grip tape along the top and back sides of the steering wheel. This is hard on gloves, but it did work for me for a while.
Also, is the steering wheel itself too thick for her hands? Can you find a skinnier steering wheel, maybe? That will allow her to grip around it farther?