Does a full-amount of effort seem to be there? I've had several students over the years with high IQs and plenty of potential, but they would just zip through homework and class assignments with little attention to directions or details. Their grades would often suffer as a result. They were absolutely capable of doing the work at an A-level and they understood the concepts, but they were underachievers. However, if you feel like she's honestly putting forth effort and simply not understanding or not able to communicate her understandings to others on her assignments and assessments, some type of learning disability is certainly possible.
Now, depending on which state you live in (if you're in the USA), she may or may not meet the definition of a student with a learning disability. Several states have used IDEA 2004 to completely get rid of the discrepancy definition when it comes to learning disabilities, so if a student has a high IQ and manages to perform relatively close to "grade level" (again, regardless of ability), he/she may NOT be eligible for an SLD identification. Just something you may want to research and be prepared to deal with.
