@Ganesh. It would appear that you have been misinformed, or misunderstood vaccine information that has been given to you. Your post contains several issues worthy of clarification.
1. MMR vaccine. The current schedule for MMR vaccination is first dose at 13 months, roughly. A second dose is usually offered at school entry age. This second vaccination is NOT a booster. Studies have shown that around 2-5% of recipients of a single dose of the MMR vaccine fail to exhibit ANY immune response for Measles. Therefore, offering children a second opportunity to develop an immune response is a good idea, and since such diseases are most often communicated when mixing in a school environment, it makes sense to offer a second injection just prior to entering the school system.
2. Pertussis or Whooping Cough vaccine. If your health professional told you that it was impossible to contract Pertussis following the vaccination, then they were technically in error. The vaccine does however offer substantial and significant protection against catching it at all, and most certainly reduces the severity of the infection if the vaccinated child did contract whooping cough. So you should be thankful on your daughters behalf that she had received the vaccination and therefore benefited from the protection in minimising the effects of the disease.
-ctd-