Are my guesses all right?
Sheila continued to work after she had her baby.
This is the simple past, and it means that she continued work after bearing her child. In English, we use have a baby idiomatically to refer to the act of birthing. Since it's in the past, it means the birthing is complete, and after tells us she did not continue working until after that. The two events are grossly contemporary, both being at some point in the past. Sheila returned to work relatively* quickly; there was no extended period of absence, though we don't know how precisely long it took.
Silvina continued to work after she had had her baby. (Longman Contemporary)
This also means that she continued to work after bearing her child. However, the use of past perfect places the two events at greater remove by indicating they occurred at different times; the past perfect event occurs distinctly before the simple past event. With the simple past, it's possible for the two to happen consecutively, but not so with the past perfect. It's a subtle difference, but we can infer that the time between child birth and continuance of work is likely considerably greater than in the first example. Here, Silvina did not immediately return to work after having her baby; some non-trivial amount of time passed, though we don't know how much.
* - Relatively means different things to different people, and when said about different people. I'm being intentionally vague. We often play a bit loose with the language and depend on the context for nuances. A week's leave to recover from childbirth might be unusually long for one woman (maybe she really loves her work); conversely, a month's might be not nearly long enough for another (perhaps her job requires strenuous physical labor).