house trained german shepherd

Question
My german shepherd is 4 years old and has been house trained since she was a pup. She has recently started having bowel movements on the floor every night and during the day. She is taken outside just before i go to bed at night which is any where from 11 to 12 at night. I am up during the week at 7 am to go to work and she has already had a bowel movement on the floor. She knows it is wrong because she cowers in the corner when she hears me coming down the steps. If I go out somewhere in the evening even just to go the store and am gone for 15 minutes she has already done it on the floor again when i get back even though i have taken her outside before i left. Any help with this would be greatly appreiated.

Answer
Have you talked to the vet about it?  It is highly unusual for a 4 year old to do something like that.  If it is a physical problem, no amount of advice from me will fix it.  

If the vet doesn't find a problem, review anything else that may have changed in her life.  Is she suddenly at home by herself more?  4 years is a little old to be starting pack status challenges.  Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog.  Life is much easier if the 2 legged pack members outrank the 4 legged ones.  You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/