Must a woman who was in the state of postpartum bleeding (nifas) make up for the seven days during which she did not pray after her bleeding stopped, under the assumption that she was not to pray until after forty days?

There is no minimum limit for lochia (postpartum bleeding). Whenever a woman experiencing lochia becomes pure (stops bleeding), she is obligated to perform ghusl (ritual bath) and pray, even if it is before forty days. The woman who abstained from prayer for seven days after becoming pure must immediately make up the missed prayers, performing the five daily prayers for each day until she completes the seven days. If there is difficulty in making up the prayers all at once, they can be performed in stages.