From the symptoms you described it soundls like a low grade mastitis with a
plugged duct (that pimple you see on the nipple). See if any milk flows
around the pimple or through it. Usually once the plug is gone the affected
duct will drain. Watch the breast for color changes and localized pain as
other indicators of infection. I have seen  moms without fever right before
abscess.
Also if she has mastitis, it may be what we call in our clinic *decending
mastitis* meaning that it came from within the body and is the secondary
infection site. Mastitis without nipple trauma is a red flag for an infection
elsewhere. With our clients it's usually the uterine lining.
 Ascending mastitis occurs when there is trauma to the nipple and the
infection enters the breast from outside the body. This is the most common
type of mastitis.
By the way did this mom have a C/S? Prolonged ruptured membranes?