I'm not sure if putting poops in it would attract her to wee in it - she might just think you've stolen her poops lol! If you've already got a sand bath, then maybe try a litter tray as well - somewhere else. The sand soaks up the pee smell quite well, so yes maybe you did remove all her scent a bit too quickly and she forgot about it. If she starts using the litter tray (or sand bath) I'd just scoop it out once or twice a week. I empty Charlie's potty about every 5 days. It's kind of instinctive for us humans to want everything clean all the time, and hamsters are also quite clean little animals, but scent is their road map - they don't see well and use scent to mark familiar routes and places, so if the scent keeps disappearing they get confused and a bit lost. When they crawl along on their stomachs they are scent marking so they can find their way back.
I'd say, if you can't find any wet substrate I wouldn't worry until you can smell it
