That's great that she's stable and you were able to get her checked out. Before getting a duckling though, really think through what it will take to care of them - where they will live, what they need for feed, vet care, etc. Ducks can live beyond ten years and can be expensive, can require costly medications and a lot of research and time often needs to be spent on their ailments, which can be many, so make sure that you really want to put in the effort and money before adding another one. Also, be aware that ducklings are often not sexed and you might end up in the same position if you end up with another male. It's a big decision, and if you're not really committed to wanting to go to all the effort, you might still want to consider leaving her with the rescue. I have a good set-up for my ducks and put a lot of effort into preparing for them before I got them, but it still at times can feel overwhelming when they're sick or when I think about just how many years of duck care I have ahead of me.