My daughter's sch asked for her Tdap booster.?

Why would my daughter need a booster from ALL three (Tdap) vaccines if she just got the Tetanus vaccine last year? she is old enough without the Pertusis and the Diphteria is not as alarming like in the 1900s? I am a person that do not put every little thing that the schools or doctors ask, so the pharmaceuticals and HMOs could make money out of it, only if I see that my children really are going to benefit from it. My daughter is highly allergic to many foods, artificial flavors, artificial color, and flavor enhancers(msg etc). She gets from rashes to throat closing and hallucinations. Her food intake is only organic. So would they restrict my daughter from attending classes, and How do I avoid the unnecessary vaccinations?