Is the woman who abandoned her friend, allowing her to fall into fornication, considered sinful, and what should she do now regarding continuing to guide her, despite the negative impact of her words on her?

After you have advised the woman who informed you of her intention to commit adultery, you have fulfilled your duty and cleared yourself of responsibility; because if a Muslim enjoins good and forbids evil, he is not harmed by the misguidance of others, as evidenced by the Almighty's saying: "O you who have believed, upon you is [the responsibility of] yourselves. Those who have gone astray will not harm you when you have been guided. To Allah is your return all together; then He will inform you of what you used to do." [Al-Ma'idah:105].

We advise you to sever ties with this woman, due to the danger that might drag you into what displeases Allah, and she might not even be a woman in the first place. We also caution that it is not permissible for a person to disclose their sin except for a valid purpose, and mere emotional release is not a justification for that.