Hey Ginasyahoocom,
I looked up Neurontin. According to http://www.drugs.com/neurontin.html, "Neurontin affects chemicals and nerves in the body that are involved in the cause of seizures and some types of pain." My impression is that the doctor is treating the pain. I assume, I hope, you daughter-in-law stopped taking the Wellbutrin. In my mind, arm pain is a significant side effect. It's a good medication, but perhaps not for your daughter-in-law.
As a family member, you may be of help to your daughter-in-law by doing some research on the internet. You can use a search engine - http://www.google.com/ is a good one - to learn more about Wellbutrin, and then do a second search on Neurontin. As your daughter-in-law reviews the information, she may find it helpful to list questions and bring them to the attention of the doctor at the next appointment.
I hope your daughter-in-law does not become too discouraged. There are many medications available to treat her ADD. If she doesn't feel the doctor is adequately responding to her questions and concerns, she can seek out the care of a specialist, in this case a psychiatrist, or if she's already seeing a psychiatrist, she can look for a different psychiatrist. That said, the current doctor appears to be responding appropriately to her needs.
Winnie, an adult ADD advocate