Muslims scholars agreed that it is prohibited for a menstruating woman to pray, whether that is obligatory prayers or supererogatory. Based on this, if a woman does that she has to repent to Allah and to seek His forgiveness for what she did.

There is no minimum for Nifas (postpartum bleeding). A woman may become pure from Nifas one or two days after giving birth. When a woman becomes pure from Nifas, she has to do Ghusl and start praying, even if that is before forty days have passed. As you did not pray for seven days, even though you knew that when a woman becomes pure she has to pray, then you have to make up the days that you missed.