Some years ago, I realized that dealing with my homosexual lust was the same as anyone else's struggles with heterosexual lust. The principles that work for straight Christians are also effective for believers with same-sex passions. The same principles apply to the homosexual man who is dealing with these issues. The same principles you'd share with her can be effective in her untangling her emotions toward another woman. The same principles of separation, focusing on spiritual growth and cleansing the mind apply to both situations.
Homosexual activities are fornication or adultery, just like any sexual sin.
Homosexual fantasies and lust are dealt with in the same way as heterosexual lust. Dealing with it in that perspective makes the situation less mysterious and intimidating. Finally, address root issues. For years, I had focussed my attention on the issue of my homosexual feelings. Many believers dealing with this issue have the same attitude.