It could be from stress and her feeling cruddy. It would be ideal to drop a urine sample off at the vet just to be sure there is no infection. Go back to the basics with her for a few weeks if there is no infection and she should get back on track. Lots of dogs regress when they hit adolescense (9-18 months) and need a refresher...not a big deal. Some positive reinforcement for the right thing and a little supervision/confinement will help them get back on the program.