Is there sin upon her who aborted her fetus in the sixth month, then threw it in the trash out of ignorance regarding the obligation of burying and shrouding it?

Discarding a fetus whose form has become apparent into the trash is a mistake for which repentance is due, because burying it is obligatory, and it is inconceivable for someone living in Islamic lands to be unaware of the obligation to bury it. The obligation was to ask scholars before undertaking such an action. If the abortion was unintentional, then there is nothing upon you. But if it was intentional and deliberate, refer to Fatwa No. 31052.