There is no doubt that reincarnation is an invalid concept. The entity of the human being does not change after death. Almighty Allah resurrects him after his death in his original form and identity and he will be judged for his actions. Allah almighty said "And whoso doeth good an atoms weight will see it then, And whoso doeth ill an atoms weight will see it then." (Quran 99:7-8)
If the miscarried fetus was recognized as a child:
(a) If she has a habit of duration, then it is obligatory not to offer the prayers and not to have sexual intercourse with her husband for the number of days that corresponds to her menstruation period. If she continues to see blood after this period, then as an obligatory precaution she should do the same for a further day. She may continue to do so until the completion of the ten days. The remaining period of discharge is considered to be as Istihadha.
(b) If she does not a habit of duration, she should observe the above mentioned rulings for ten days. The remaining period of discharge is considered to be as Istihadha, and based on an obligatory precaution she should observe the rules of the woman during lochia (Nifas) for the completion of eighteen days.
If the miscarried fetus was not recognized as a child, like if it is a clot or lump of flesh, then based on an obligatory precaution she should offer the prayers based on the appropriate level of Istihadha and refrain from performing what is prohibited on the woman during lochia (Nifas).