My lovely and perfectly gigantic German Shepherd girl does this. She has spay incontinence.
It was very bad when I first adopted her --- she would almost flood an area, so I was scared she had some horrible disease.
But it's gotten much much better -- she still does it a bit, but nothing like it was.
For her, exercise, better nutrition and a major lessening of stress made all the difference in the world.
If your girl has stress incontinence, sometimes the only thing that works is some drug --- ??? Can't remember what it is. Here, though, lots of exercise, good eats and much reduced stress (she wasn't in a great situation before) have made a huge difference.
Because she does still do it a bit, I have the sofa covered with a thick comforter and have encouraged her not to lay on the floor, but stay on her bed. That makes cleanup easy and allows her to engage in the normal indoors doggie hi-jinx.
Be sure to get her to a vet --- other things can cause this, too, I imagine --- but if it's spay incontinence, it's actually pretty easy to deal with.
