This behavior is very common in non-castrated females, depending on the stage they are in relation to their fertility cycle, they associate the offspring with theirs. Sometimes this happens even with stuffed animals and even forms milk. We call this psychological pregnancy, or pseudocyesis.
In this case, the best thing to do is to castrate your Poodle. In case your puppy is already neutered, the indicated and separate her from the Rottweiler puppy for a few days, allowing only supervised visits to have some contact until they stop this behavior. If they still persist, it is advisable to seek a professional in animal behavior.
Hope this helps.