Pain inside nail of the left thumb. Do?

My mom had an injury about 25 years ago when she was picking up a broken glass and a part of it went inside her left hand thumbnail, she told me that she has had the glass pieces removed from her nail 2 times but still once in a week she has a sharp pain inside her nail. And one thing i want to tell is that she doesn't do much work with her left hand as if the side where the injury was is accidentally pressed or touches something the pain starts again. The pain is very intense. I want to get her checked but I don't know what to do? Which doctor to go to, as i think that something is still inside that nail which is triggered whenever she tries to do work with her left hand. Please suggest something, thanks