WISC IV goes up to age 16 years and 11 months. So, once a child turns 17, he has to be tested on the adult test, WAIS IV. However, WAIS IV starts at exactly age 16 and goes up to very old age. So for the one year between age 16 and age 17, one has a choice of whether to test on the WAIS or the WISC and WAIS should be slightly harder.
So, obviously in your case there is no choice and your dd will be tested on the WISC. However, some here say (and I can't comment on this at all) that WISC becomes too easy for gifted kids starting from early teens. The test being too easy is good if you are looking to qualify for GT programs. However, if you want to document LD issues, having some headroom and thus a harder test is probably better.
