Love her, and tell her and testify to her how Jesus loves. Ask the Holy Spirit to reveal to you what to say and when to say it. Even ask for a sign, a miracle for her, that can break through her unbelief.
But above all, let the love and joy and peace of the Gospel fill your life, and don’t be anxious and troubled and fearful.
Also, consecrate her to Jesus through Mary. Only God knows her heart and He is more eager and able to change her than any of us. Entrust her eternal life to God. And as you said, in exchange, pray, fast, offer sacrifice, and become holy yourself.