housebroken dog randomly eliminating in house

Question
My male dog and I recently just moved back into my boyfriends house with him and his female dog. The dogs have known each other for a long time, and have always bonded well. Recently the female dog has been randomly pooping in the house after she has been let out. She is not usually left alone for a long period of time and is let out on a very regular schedule. We have been confining her space more hoping that would prevent it, but have only had some luck. Initially I thought it was because of the change of environment, but she has now had a regular routine for a couple months. Both the dogs are spayed/neutered, and had previously not given us any problems like this. Our female dog is taught to ring a bell if she wants out, but sometimes she will go before I get up without doing so. The male dog does not give us any problems with not pottying outside, and I am worried that he may think it is OK to do this because she is.  I would love any advice on how to fix this problem we are having with her. Thank you

Answer
Since she's developed a pattern of eliminating in the house over the last couple months, I would confine her to a crate unless you can pay 100% attention to her.  She should only be allowed freedom in the house if you're sure she's peed and pooped outside.  You have to go outside with her and confirm that she's done her business.

Also, be sure that your feeding routine isn't contributing to the problem.  Since there are 2 dogs in the house now, don't allow her to get into his food (and vice versa).  Be sure she's not overeating.  Put down their food bowls twice a day and pick up what they don't eat after 10 minutes.  If they have regular feeding times, you should be able to predict when she'll have a bowel movement.

Make sure your yard is kept cleaned up of waste.  She doesn't have the yard to herself now and may be stressed about the new boy's poo in the yard.  

Just some thoughts for you.  The big thing is to prevent mistakes!  Good luck.  Let me know if you have any questions.