Night terror

I don't know whether you'll be able to help, or ask someone (!), but over the past few months, my three-year-old Collie has taken to pooing during the night.

I feed her at about 6pm, she goes out before I go to bed and I have even taken to using a spray on the mat/floor in the kitchen to deter her, but no good. I am at the end of my tether and have no idea what to do!

Any suggestions would be gratefully received!

Julia Graham, via Facebook