Welcome to the Wefugees Community and thank you for sharing your question.
If you want to apply for a visa based on your relationship, you either need to be married or prove that you plan a marriage in Germany. Unfortunately, there are no visa categories for unmarried couples. Whether there are other opportunities for her to migrate to Germany is difficult to say without knowing her background. Does she have a formal/higher education? Is she maybe even trained in a field in which German employers are constantly struggling to find staff?
Regarding the child: I am not familiar with laws and regulations in Ghana. However, I assume that the child‘s father may need to approve the process at least.
I hope this helps and please don’t hesitate to get back to us with any further questions.
All the best,