It all depends on the skin. My grandma has three and one needs a medicated shampoo every week and the other two just get them whenever. You just have to be carefull with leaving soap in the folds. The poor things are not blessed with the best skin!
Well I'll be the first one to admit I don't know very much about Shar Peis, but from everything I have heard I would think frequent bathing would be a must. With all of the folds of skin, I know it is a common thing for Shar Peis to collect all kinds of bacterias and dirt in their skin folds that can cause skin infections. Like I said I have never owned a Shar Pei but I would thing washing them frequently would be a must. Perhaps is you do not want to bath her so often, you might try getting some of the doggie bath wipes, they are really great to help with odor and just cleaning them up a bit between baths, I would think if you wiped out her folds often this would help cut back on the number of baths she would have to have.
Actually it is just the opisite with shar-pei's. Their folds need to stay dry. When they are wet bacteria grows very quickly in their folds. So unless they are suffering from a skin allergy which is very common with the breed. Then you need not to bath them much at all. I would say every three months. Of course if they smell then more often. Also if you are having skin problems make sure you are feeding a food with no by products or corn in it. They can not handle it.