Why is my child always tired, and she has joint pains that sound like arthritis.?

Sleep disorder. We see this with poor sleep patterns. With lack of sleep - fatigue ensues and this can lead to systemic aches and pains. This could be muscle pain and we see this with fibromyalgia. When she gets evaluated these will be some of the things she will be evaluated for. Other issues include joint evaluation for arthritis, and bursal and tendon examination.
Need more info. How old is your child? How long has she been having these symptoms? Does she get the appropriate amount of sleep at night for her age? Does she snore at night? How much does she weigh and how tall is she? Do her joints look swollen? You should probably take her in to be evaluated, there are so many possible explanations.