Changing the saddle is the last resort after checking position, which means height, angle and distance from bars, all adustable.
Next check that she's wearing decent cycle shorts with the pad next to the skin. Next check that she's not over-dressed and getting hot and sweaty, which will cause chafing.
Lastly if it's a fat squidgy saddle, ignore all the above and throw it in the bin. Get her a proper women's saddle like a Charge Ladle and get it set up correctly, as above.
Fat squidgy saddles are the Devil's work as they make you sweat and allow your supporting pelvic bones to sink in, transferring weight to soft tissues.