Too many variables to just answer. As others asked why did they sneak out? What did they do that might make it worse? What other discipline issues have you had? How did she do in school?... Sometimes the best thing to do is take a deep breath, look at the child as a whole and have a long talk with them. Find out why they did what they did, what did they think of what they did and then ask them what they think the consequences should be. Limit the time of the punishment, if you make it too severe at the beginning you will be swayed to cut it back later. Then you will look weak. Its better to give her 2 weeks of punishment you are willing to enforce then 4 weeks that you will forget about after 2 weeks.