Is the friendship between two girls who cooperated in evil, then repented and repeated repentance and sin several times, then returned to draw closer to Allah and memorize the Qur’an, permissible in Islamic law, and can they continue it or must they separate?

The friendship between the two girls is sound and acceptable, as long as their repentance is sincere and their situation has become as described in the question. It is an expiation for them for past sins, and they must cooperate in righteousness and piety and avoid forbidden things. However, if their gathering together once again becomes a cause for cooperating in sins, then it is obligatory for them to separate.