My wife delivered a baby 4 month ago & now her wrist hurts when she move it a certain way. her friend told her it's because her delivery. is it normal?

I do not think so: This condition can occur in postpartum women due to the position of the thumb in abduction for extended periods of time while holding a baby. Additionally, prolactin levels in new mothers who are breastfeeding may have something to do with it. Often, if a woman stops breastfeeding, de quervain’s will disappear.

Wrist pain: Wrist pain worsened with certain motions in a 4 month post partum female makes me think of a form of tendonitis called dequervains tenosynovitis. This leads to wrist pain at the base of the thumb. If so splints can help, nsaids can help , cortisone can help.