My daughter has a rash on her arms and stomach, she has had it for going on two weeks and wont go away. She does say it hurts. What could it be?

Need a visual. There's a lot that depends on other factors, such as how old she is, what she's been in contact with, and whether she's been ill lately. Rashes like this could be a contact dermatitis, eczema, or an infection. She needs to be seen to be treated properly.
Several things. It could be a staph/strep infection, or some other bacterial cause. It could be a virus, such as zoster, molloscum or others. It could be eczema, or related to allergies or contact, although these tend to be more itchy than painful. Bottom line: have her doctor take a look. It may resolve on its own, but it may also require treatment.