My little girl is just learning how to wipe herself how is the best way to treat her rash?

Emollients: Otc emollients such as desitin (zinc oxide diaper cream) or a&d or other moisturizing cream should help with the rash, if it does not help within approximately 7 days perhaps you should check with your primary care provider to insure that there is not some sort of yeast infection or other phenomena going on.

Wipes & 'sitz' baths: It is hard for young children to master the coordination for cleaning well--it requires pretty sophisticated motor control! premoistened "diaper" wipes do a better job cleansing than tissue and are much gentler. I'd also suggest a brief "sitz bath"--just water with no soap/bubble bath--a couple times a day. This will keep her clean which is key, and if necessary, a zinc-oxide based cream can help.