Being totally honest mate i dont think it's the dogs fault. There is something wrong with her bowl control.
Has she had any sort of impact around her rear i.e. a hard boot up the backside or clipped by a car etc?
This can sometimes cause dammage to the nerve endings and cause dogs / cats to have very little control over there movements.

Our boxer has around 4 craps a day and we feed him morning and night with Bakers Complete.

Where are you in Scotland? Can put you onto a really good vet who has dealt with all my wifes boxers in the past if you are local?

Id try the walk thing before bed as our's wont foul anywhere but the strip up the side of our drive so we take him out then he dumps there when we come back before going back inside.

I have never known a boxer not to train easily so id guess thats not the issue so i wouldnt be to hard on her.

Hope you get it sorted.