You will need to remove her from this environment immediately because she is either going to be seriously hurt, killed or prevented from eating and drinking which will eventually kill her from stress or malnutrition. You have interfered with a family and this is not going to get any better. In fact, shortly, the young swan will be banished from the lake due to the upcoming nesting season. If you can find another safe environment, you may even be able to pair this young juvenile in about 6-8 months if the bird is a male and your female is not more than 2 years older than him.

Otherwise, you will need to build an enclosed pen so that predators cannot climb over the fencing and into the pen or dig underneath. The swan should be brought in around 2PM and let out about 9AM. Some pond time is better than being killed. This will be useless if the coyotes start roaming in the daytime in search of a midnight snack for them. In this case, your female is not safe. Therefore, another safer habitat is highly recommended.

By the way, where are you located? The Regal Swan