There certainly are reasons to be concerned if there is large gap between how a child performs on tests that are designed to measure school performance (e.g., achievement tests) and tests that are supposed to measure intellectual capacity (e.g., IQ tests). But it's just not appropriate to leap to the conclusion that learning disabilities are the cause without more careful analysis of this child's performance. This is especially true in kindergarten. First of all, the range of children's pre-academic and academic skills is very wide in the early grades, since children develop at such different rates. Because of this, it's inappropriate to give much significance to achievement tests results at this age, since so much of the variance in scores is due to difference in development, and not to "problems." Furthermore, IQ tests, even though they are well-respected tools, are least valid when used with very young children for the same reasons.
It is important to note how well young children are acquiring readiness and early learning skills, and to look for the early indicators of learning disabilities. Clearly, difficulty recognizing letters could be a cause for concern, but more information is needed in order to diagnose LD. Don't forget to identify this child's strengths. He might be gifted verbally, but relatively slow to develop visual perceptual skills required for letter identification. For a very helpful selection of resources and checklists that will help your friend and her child's teachers determine whether or not the child has a learning disability, I encourage you to go to: LD Online.