Point 1: circumstances and experiences during pregnancy have an influence on the later development of the child, do it is not completely irrelevant. However, I agree that the baby cannot leave the mother until birth, so "imprisonment of the baby" is a very week argument.

Point 2: not only the baby, but the mother as well!

Point 3: the defendant claims, that she was attacked and defended herself and the baby with a single shot. There is no verdict in the case, yet, so far she is only indicted. That means she has to be considered innocent until proven otherwise.

In other words: if she is convicted, then you are right. Until then, the child should stay with the mother, except if there is any indication for neglect or mistreatment. An alternative might be the father, but you should have very good arguments to separate mother and child, and for me, that means you should have very good arguments to keep the mother imprisoned until the process.