The Bible doesn't answer all our questions about heaven—but no, your friend won't look sad there. The reason is because all of the problems and heartaches she experienced here will be behind her. In heaven, the Bible says, we will be forever in Christ's "glorious presence without fault and with great joy" (Jude 1:24).
Not only that, but in heaven we will be free from all evil, and we will never again be touched by anything hurtful. Think of it: Not only will we be free from evil, but we won't even fear it, because it simply won't exist. Anxiety and insecurity will never touch us—which is one reason why heaven will be a place of great joy. In the familiar words of Psalm 23, "Yea, though I walk through the valley of the shadow of death, I will fear no evil: for thou art with me" (Psalm 23:4, KJV).
But there is another reason why we will be supremely happy in heaven—and that is because we will be with Christ. Then we will realize just how much God loves us, and how much it cost Christ to purchase our salvation. We also will rejoice in God's goodness to us during our lives on this earth.
The real question, however, is this: Do you know—really know—that you will go to heaven when you die? You can know, by committing your life to Christ and trusting Him as your Lord and Savior. Open your heart to Christ without delay.