Can a Girl of 12 get Pregnant?

To Answer that question we need to look at some Factors.

Sexual Development

At the Age of 12, a girl would have developed the sexual organ in her body. Talking of the Ovaries and Egg, the Womb would have developed but the wall of the womb might not be that thick due to Age or Something.

At the age of 12, a girl would start having sexual Feelings

At the age of 12 a girl might have started having her menstruation.

So if a girl of 12 have inter course with a man, a pregnancy should be expected. So the Answer is Yes.

Evnironmental Factor

If a girl of 12 live in a slum where every cats and dog are having inter course in her presence or having inter coourse with her, it will prompt the development of all this Organs and would grow Faster than Normal.

So yes. A girl of 12 can get pregnant