
Hi Christine,
Perhaps something has happened to make her associate her toileting differently at you friend's place :-( It could just be your friend hasn't been as quick off the mark with her as you and has failed to clean the area with a biological solution so not properly gotten rid of earlier smells.
I think I'd advise your friend to go back to basics with her - as if she were a baby puppy again. Actually always physically accompanying her into the garden (preferably without her other dog), waiting however long it takes for her to "perform" and using an appropriate command word (hurry up, busy, be quick etc) at the crucial moment ;-) then make a huge fuss of her.
She is probably using her time in the garden with the other dog for games only.
HTH, Regards Teri