I was born in South Africa and would like to know whether I qualify to apply for German citizenship through ancestry.

My great grandmother was born in Germany in 1872. (Have her original baptism/birth certificate. Her parents left for South Africa and from there my line, i.e. she is my mother's grandmother and my great grandmother.

Any help will be appreciated

Nope... too much separation. If it was your mother... it would be different. The laws have changed.

German nationality laws were changes in 2000, irrespective of blood ties, in order to receive German citizenship you must reside in Germany for six years and be fluent in the German language.