What do I do? My 6 year old stepdaughter lies about EVERYTHING..?

First of all she needs to be taken off the medication. It is not suitable for children. Does she live with you and your husband or is she shuttled back and forth between homes? Divorce, or the death of a parent can cause all kinds of emotional problems for kids and she may need to talk to a counselor about her feelings. This kind of behavior is not normal for a 6 year-old and the sooner she gets help the better, and family counseling, and parenting cles may be in order too.