Indian runner duck died suddenly

[Runnerduck3737]

I have 2 ducks, a female Indian runner duck and a male mallard duck. They're about 7 months old and I had them since they were ducklings. I bought them from rural king (a farm and fleet store). Last night I left my house and they both seemed fine, absolutely nothing abnormal and then I came back around 16 hours later and I found my Indian runner duck dead on her side, eyes open, and the bottom of her bill was a blue color. The mallard seemed fine. There was no blood, her feathers were perfect. I know that mallards can be sexually aggressive so I've been watching since his male feathers came in to see if he would be too rough with her but I haven't seen him touch her and she never seemed afraid of him, they did everything together. I feed them mostly commercial duck food and some mealworms with grit that I mix in and then occasionally some vegetables (the last thing I gave them was corn) she recently started laying really good eggs every other day so I don't think she was egg bound or anything, and they have access to water that deep enough to put their whole heads in. Unfortunately it would've costed me $600 total to get a necropsy and cremated and that wasn't an option for me so I'm just getting her cremated but a little peace of mind of knowing what could've happened would be helpful.
Thanks

 

[nuthatched]

I'm sorry to hear about your duck. Were they outside?

 

[Runnerduck3737]

No I keep them both inside but they did have a pretty decent amount of supervised outside time. I'm in Illinois so it's really cold out but once it warms up they were both going to be moved outside