Is marrying the girl who repented of her shameful past, which I know about and which previously caused me harm, good for me or will it hurt me? And is abandoning her after her repentance considered an injustice to her?

Acquaintance between young men and women is a gateway to evil and corruption, and the claim of offering mutual advice and cooperating in good therein is false. If the woman expresses her desire for repentance and seeks help, then assist her within the bounds and controls of the Sharia, and entrust this matter to a righteous woman. We advise you not to marry her and to seek someone else, unless she repents, becomes upright, and your heart is reassured of the sincerity of her repentance.