Is it permissible to marry a woman with whom the questioner committed Zina, and then discovered that she had committed Zina with someone else six years prior, out of ignorance of the religious ruling, knowing that she is remorseful and wishes to repent and be veiled?

You must repent to Allah Almighty from committing adultery: by desisting, regretting, and resolving not to return to it, while concealing it and not publicizing it, and avoiding the causes of sin. If both of you repent with a sincere repentance, then there is no blame upon you in marrying her, for repentance erases what came before it. However, if the woman has not repented or you find doubt in her matter, then leave her and seek someone else.