HI! Oh, I remember those days! lol

Is she in daycare? How is she doing with potty training when you are not there? IT could be a lot of things, if it continues, you should take her to her doctor, sometimes it is a urinary infection.
But I would guess it is anxiety, kids tend to backtrack on their physical progress when something stressful is happing in their life.It could be you going back to work, or her babysitter,a growth spurt,or who knows? Maybe the person she is staying with while you are working needs to remind her more and ask her if she needs to go. Good luck, and don't worry this isn't forever. ;-)