Limping can be an indicator of abdominal pain, for future reference. Usually, liver and kidney issues will present with a gradual yellowing of the urates from their typical white all the way up to bright tumeric yellow once it's more advanced and they're getting close to organ failure.
Its definitely a tricky thing to pin down once their organs start failing, and I'm not very familiar with duck breed characteristics, but could she have been from a poor background genetically, or are runners bred to be short-lived?
I know with chickens, it's very hard to outrun a genetic disposition for self destruction.
We're her fecal samples ok? Nothing extreme there aside from the bacterial infection?
When there are other things going on, they essentially become immunosuppressed, allowing what would typically be a rather mild infection to run amok and cause lots of damage.
I had an anemic hen (1 year old) that ended up with necrotic enteritis from coccidia, of all things - the thought from our exotics vet was that something else was going on that allowed the coccidia to get out of control.
We didn't do a necropsy - she was a pet and the rest of the flock were healthy. I had my suspicions about her breeder though - she made it the longest out if all her hatchmates, but they all had weird things wrong with them from the start. Pretty sure there was a bit too much inbreeding going on.
