I Guess I Have To Retrain My Abbey Dog Again??

Besides my two chihuahuas, I have a chi/terrier, named Abbey who is starting to give me a little bit of trouble these days.....and I have yet to discover what's going on with her. Every night, my chis sleep in their kennel, actually they love it and my Prissy will come and get me to tuck her in each night. Prissy likes to have the cage door shut with a towel on top of the cage covering her door, I suppose she just likes her privacy. (lol). Shorty has his own kennel and retires there over night as well, but Abbey, she has the run of the whole front of the house, with her bed in the living room corner between the two sofas. I have pee pads down in the same spot down the hall way and every single morning we wake up and Abbey has pooed in the living room and not only that, it's on our rug. I don't know why. She knows good and well where the pee pad is and normally uses that during the night but all of a sudden now, she has decided that our living room carpet is where she's supposed to go. We caught her yesterday in the act and scolded her, but again this morning, there was pooh. Maybe she needs to start sleeping in the bathroom until she learns all over again where the pee pad is. I just don't know what's going on with her these days. Any suggestions on how to retrain a dog who's about 5 years old and has always gone potty in the right place until now????