My new 2yr old dog wont stop messing in the house :S?

I just adopted a new dog from the pound. Shes 2yrs old and is very good when Im watching her, but when Im away or sleeping she pees and poops in the house even though I take her out often. How do I get her to go outside and not inside? She also chews things, but again only when I'm gone, could this be angsiety after only having her for a week?