Maybe you could try it in reverse and take the pee pad outside when she is going pee and keep her on the leash. Have her pee on the pee pad and praise her like all heck. Have her keep peeing on the pee pad until she chooses all on her own to go on the pad. Then move the pee pad inside (you could even do this in stages by moving the pad closer and closer to the house).
I think you did such a good job of potty training her that she is scared to go potty inside and is holding it until she absolutely bursts! The pee pad means nothing to her, which is probably why she is looking so confused. Show her that it is okay to pee on the pad by putting it outside and then bringing it inside. Hopefully this will clear things up for her. And congrats on being such a good potty trainer!
