NWEA uses 95th percentile to identify as gifted. I would ask for them to reconsider based on their own data. If they do not want to do so, I would ask who has the authority to make such a decision and go from there.

http://www.nwea.org/support/article/997

Unless your school has some sort of HG/PG program, 138 is extremely high. If you cannot get them to classify her as gifted, then you'll need to work on her individual academic needs each year with each teacher.