I would stop the ice water. It can shock the body and she could have other issues.
What feed is she on? What's her set up like? It almost sounds like overheating and she's panting to cool down. The room temp would be hot for humans.

I'd also suggest less time in the bath tub. She might not seem like shes over exerting herself, but ducks do silly things. Normally ducklings swim or splash a little and then run around to jump back into the water they aren't in constantly for extended periods. Is this your only duck?