Is it possible to receive the DTaP too many times?

My daughter is 8 years old with Idiopathic Genetic Autoimmune Hemolytic Anemia. Anywho her immunologist wants to test her immune system by giving her the DTaP then testing her blood in six weeks to see how her immune system reacts. Here are my concerns. First everywhere I have read online states clearly that DTaP is not licensed for children 7 and older. Also if I let her get this round of DTaP it will be her now 7th time receiving it. Does anyone know if its possible to get too many injections of the DTaP?

[Vaxpro1]

DTap is not licensed for children over 7 years, After 7, they receive the Td (tetanus/diptheria) vaccination every ten years thereafter. There is a new vaccine called Tdap, which is for older adolescents and adults needing a tetanus booster. It has a small amount of Pertussis vaccine in it. Since a persons last vaccine containing pertussis is at age 7, they reccomend the Tdap be given as a one time booster to boost the pertussis immunity in older adolescents and adults. After childhood, you should not receive a Td vaccination more often than 3-5 years apart.