Your duck sounds like a lucky girl!
I have 8 Cayuga 'girls' and two Cayuga drakes (absolutely one more than I need). I have four blue Indian Runner ducks.
I know we have had (and probably still do have) foxes on the hill across the street and we hear coyotes some nights.
I've read that black (and grey?) ducks are harder for predators to find - not that I'm relying on that alone. These ducks are a large breed and with 13 of them, there is a better chance that someone is on the lookout more of the time. We have two dogs that leave their scent outside and are on the prowl all day (but inside at night). The ducks have access to the pond, (and some fairly small floating islands), which may give them an extra level of protection. And maybe we've just been lucky so far . . . We do plan on fencing the entire five acres this summer. [I still have hopes for a pig or two in the future, or even a dairy cow or two, but don't tell my husband!]
I usually leave the chicken run/coop door open during the day and close it at night. I have the duck food (and a large waterer) inside the chicken run so the food stays dry and the ducks have to enter the run to eat - hopefully becoming more comfortable inside.
When I went out about 4:00 p.m. yesterday to close the door, I found that the wind had blown the door closed earlier in the afternoon. The chicks were all inside already. I opened the door, stood thirty feet away and watched as the ducks went in to eat. I was able to close the door before any left, so the ducks spent the night in the run/coop.
When I went out this morning, I found only three eggs on top of the pine shavings. [The ducks rejected the nest boxes I've given them so far. They've preferred making their own nests at the edge of the yard or in straw in the garden.] When picking up the eggs, I decided to fluff up the pine shavings a bit (I'm trying the deep bedding method and the bedding is still quite fresh, clean, and fragrant). Upon doing so, I found a dozen more eggs.
I suspect the ducks have been sneaking in to lay and that the eggs have been covered, perhaps by the chickens or maybe by the ducks? The bottom layer of pine shavings was cool (the coop is on blocks). I'm going to eat the eggs, since I think they are probably still reasonably fresh. I won't sell those eggs though.
Even though there is some question about how much use the ducks make of the coop, I'll try to photograph the run/coop today and put the photo online. I inherited the coop from my husband's first wife and the run is new this year. The materials for the run cost $1,000 according to my husband. As he points out "That's a lot of eggs!"
Good luck to all protecting their ducks from harm.