Yes, you will run into these things having the "step mom" title. #1, she is hitting a rough age. As for the lying, you simply need to get through to her that lying only makes the situation worst. She needs to understand. #2, she is going to test her boundaries with you. She sees it as, you aren't her mother. Let her know where you stand. You can't always be the friend. I learned that the hard way. She needs to know you are an authority over her and that is that. As for the short time you have her, yes, it is hard to come up with proper punishment. Here is an idea of something I do with my own children. We do positive reinforcement in our home. We have tickets, a treasure chest, and a chart. you decide what is to be on that chart. Each time they follow the chart or when you catch her doing something positive, give her a ticket. At the end of the day, you let her pick something from the treasure chest. Put simple little things in the chest. Candy, trinkets, etc. Now if she is wanting something big, well you decide how many tickets that is worth and she can save her tickets for it! NOW, if she lies or misbehaves, well then you take a ticket away from her. This may help you! Good luck