Is it permissible to abandon a female friend who has repented from a previous relationship, and am I sinful for cutting ties with another female friend due to the exposure of her illicit relationship?

If a girl repents and becomes righteous, it is not permissible to abandon her due to a sin she has repented from. However, there is no harm in ceasing to associate with her without abandoning her. As for a girl who has not repented from an illicit relationship, there is no harm in abandoning her, especially if harm is feared from associating with her. Abandoning those who commit sins revolves around what serves the best interest. If abandonment is beneficial in bringing them back to rectitude, or if associating with them harms one's religion or worldly affairs, then abandonment is preferable. If maintaining connection with advice is more beneficial for them, then that is preferable.