Yes, of course it’s wrong for her to be lazy. It would be wrong even if she weren’t a Christian, because someone who fails to do his or her job is actually stealing from their employer (by taking money for work they didn’t really do).
But it’s especially wrong if she is a Christian, for God calls us to be faithful and diligent in everything—including our jobs. The Bible says, “Whatever your hand finds to do, do it with all your might” (Ecclesiastes 9:10). The Bible also says, “One who is slack in his work is brother to one who destroys” (Proverbs 18:9).
Why is laziness a sin? One reason is because lazy people shun their responsibilities—including those God has given them. A lazy person is also self-centered and thoughtless, constantly seeking the easy way out and ignoring the needs of others. The Bible is clear: “Whatever you do, work at it with all your heart, as working for the Lord, not for men” (Colossians 3:23).
Don’t let this person’s bad example, however, keep you from facing your own need of Christ. No matter how good or diligent we are, we still need God’s grace and forgiveness. By faith open your heart to Christ, and then ask Him to help you be an example of faith to others—including this woman.