Welcome to BYC and very sorry to hear about your drake being taken, duck is high on the menu of most predators so I hope you have a secure area for your lone female and your ducklings when you put them with her. If the weather is warm in your part of the world begin to introduce your 3 month old to your ducklings through fencing this way when the ducklings are old enough to go in with her they will have already gotten use to each other. Just remember we have to keep them safe.
Post some pics when you can.
Thanks lydia..will post some pic later..still feel sad due to my drake lost.. btw my solid white ducklings is about 3 week old..bought it from the local at my village..my drake is being snatched from its fence..i do some inspection and i found some tiny hole..and also his body..the predator maybe dug some hole and bite my drake leg and drag it out through the opening that the predator make..i think it water lizard..its very commom predator that like to eat chicken and duck here in Malaysia.