Ducks only need additional niacin for the first 10 weeks. I'm going to assume you mean wild game feed when you say wild feed. There are two problems with giving that to laying ducks. One, it won't have the calcium they need to form good egg shells. Low calcium can cause a duck to become egg bound and weak shelled eggs can break inside the duck causing egg peritonitis. Both can be deadly if not addressed. Two, wild game bird feed is way too high in protein. It's usually 24-30% protein but a laying duck only needs about 16%. Not as critical as the low calcium but still not good.
I'm guessing your duck's death was related to the low calcium. The sick duck may be egg bound. Get her in a tub of warm water because it can help her relax and pass the egg. If that is not the problem you may need to get her to a vet.
I'd take them all off the game feed and get them back on layer feed. Also get some oyster shell and offer that free choice. It wouldn't hurt to add some calcium powder to some peas or other treats they like to help them boost their calcium levels.