If one is having sex and it seems that the sperm has not been secreted in girl's vagina then if it is necessary for the girl to take pill?

How old are you?

It is always important to use protection to prevent sexually transmitted diseases and unwanted pregnancies. So yes not only should she take the pill but you should always wear a condom.

First, we need to know how old you are. Second, we need to know what pill you refer to.