Praise be to Allaah.
If the bleeding stops and she become pure, and she does ghusl after menstruation with the intention of purifying herself, then she is considered to be pure (taahirah). There is no specific du’aa’ for that, apart from the well known du’aa’s that have been narrated for doing wudoo’. And Allaah knows best .
Sheikh Muhammed Salih Al-Munajjid