Doing what makes me happy

So today I was talking to someone who I suspected was heading into some behaviors that are wrong. I gently introduced the topic, and the person didn't deny it, so I pressed a bit and asked her what was going on to which she said, "I am doing what makes me happy." I was taken aback to say the least. The thing is that this person knows what she is up to is contrary to the Word. God has given her a TON of freedom from past stuff, and she has had incredible breakthroughs that she credits directly to the Lord. Bottom line--she knows better! I thought to myself, since when is the criteria for our lives as Christians to do that which makes us HAPPY? Somehow does this excuse sin? Is God okay with our behavior because He is so thrilled that it makes us happy?! I am floored! And then I thought to myself, am I really any different? How often do I excuse myself because I want to do or say or think something that will make me happy? But wow, what a good reminder that my happiness does not change God's standard. Sin is sin. God really isn't too impressed with our idolatry of happiness. And now the question is, how do I respond to this person in a right way consistently?