There are several types of synthetic grass, ranging from the very inexpensive stuff you buy on rolls at Home Depot to the stuff you'd SWEAR was real that is put in your front yard - or on NFL fields.
At least ONE of them should be non-reactive for your girl. Even the expensive stuff could be useable ... you only need a few square yards for a potty area.
One of the ladies on another forum I haunt had her whole back yard done with the stuff the NFL uses. She has 5 Aussies and was tired of the brown spots that ruined her yard. She kept her sprinkler system, except now it's only used to rinse the yard
.