Hm, interesting. I had never heard of this. From the website:

A burial at Viden Denmark contained the body of a woman of wealth and status buried with henbane seeds, which have hallucinogenic properties and a wand as well as other objects. From these, it was concluded that she was a seeress or sorceress. The grave contained a necklace hung with three duck’s feet pendants very similar to this.

There is, insofar as I know, no place called 'Viden' in Denmark (viden means 'knowledge' and would make a strange place-name), so I searched through my library for instances where both henbane and bird's foot pendants appear together. The only example I could find was grave 4 at a site referred to as Fyrkat, or simply stated: Fyrkat 4. This was a pretty spectacular burial so it gets referred to from time to time, but I'm relying on the in-depth discussion provided by Neil Price in his book, The Viking Way (2002 edn., pp. 149ff.).

Fyrkat was one of Harald Bluetooth's round fortresses, often referred to as Trelleborg forts after the most famous example. Some of the wood used at Fyrkat may have been felled as early as 980, but it's often assumed that these forts were constructed in connection to Harald's campaigns in southern Jutland in 983. Harald died in 987, and it seems like most of his engineering projects were abandoned shortly thereafter. This gives us a fairly narrow date range for the 30 graves dug just north of the camp, including Fyrkat 4.

Harald Bluetooth was a Christian, so we can presume that most of his followers, including a substantial part of the population at Fyrkat, were Christian as well. Most of the graves at Fyrkat lack any accompanying grave goods. The excavators assumed that most of the dead were buried wrapped only in simple shrouds, which was a common form of burial in Christian churchyards across northern Europe at the time. This makes it difficult to interpret Fyrkat 4 and her role in the community. She was buried with a lot of things, which seems to have been an non-Christian habit, but she was living in a community and placed in a cemetery full of people who were probably Christians, so it seems like some form of accommodation or maybe even religious hybridity had developed there.

Fyrkat 4 was buried in a wagon, which was a lavish and rare form of burial, practiced primarily in Denmark. She had some sort of a metal spit that Neil Price and Leszek Gardela describe as staffs that were probably used for 'magic'. There was a box at her feet, a scattering of other grave goods, and a few things on her lap—the kinds of things a woman would typically wear on her belt (and not on a necklace): a knife in a sheath bound with silver, a chair pendant, three bird's feet pendants, and a few hundred seeds of henbane. The henbane seeds were discovered at the grave bottom and may have either been strewn out as a bed for the corpse or, more likely, have been placed in a leather bag in her lap, filtering to the earth as the organic materials decayed.

Price found no parallels for the henbane or the bird's feet. He was, in fact, more immediately interested in the chair pendant, which may have been seen as symbolizing some sort of high seat for the gods. Nevertheless, some interested asatru enthusiasts trumpet the henbane found in Fyrkat 4 as proof that Norse seeresses used mind-altering drugs. But this grave is unique, and because it's unique, we have no guide for helping us interpret what the henbane was doing there.

We're a bit better off with the bird's feet. Although Price found no similar pendants (and I couldn't find any in my literature either), we do occasionally find bits of birds in graves. They typically occur with other animals and things like nuts, which leads me to assume that they were left to symbolize food. But I know of two examples from late Viking Age Gotland (i.e. same time period) where wishbones were found in graves. This is especially interesting because, although Fyrkat 4 didn't wear any of the typical women's jewelry into her grave, there was an old beat-up Gotlandic brooch buried beside her head. Price also found an example of Mongolian shamans using bird wings in their rituals, and some of the other Gotland graves include specifically bird wings. These things suggest but by no means prove that the bird's foot pendants may have had some sort of association with rituals linked to the Baltic, which were themselves connected to religious practices that Norse travelers may have encountered while traveling the Russian riverways.

It's also important to note that no bones survive, and there were no typical items worn as female dress, such as brooches or a necklace. We think this person was a female because rich burials like this one were typically female, weird burials were typically female, and I believe the other fourteen or so excavated wagon graves were typically female. So it seems likely that this person was buried as a female, although strictly speaking we can't say anything about the person's physiological sex or gendered identity.

Where does that leave us? There's only one example of 'duck feet', so we don't really have much basis for interpreting what they may have meant. These were buried ca. 980-987 at Fyrkat in northern Denmark with a person we presume but do not know for certain was a woman. This person was buried with a lot of other things, including henbane, which is also unique. These things suggest she might have used them in some sorts of rituals, but she also circulated in an increasingly Christian society and was buried in a cemetery apparently alongside Christians, so we should be cautious in interpreting these items as specifically pagan artifacts.

Sorry that doesn't give you a definitive answer, but I think it's important to show why a definitive answer isn't always possible. It helps debunk sketchy claims such as this webshop's reference to a 'necklace' found at 'Viden', and it gives us the freedom to imagine how Viking Age artifacts might be made meaningful, both then and now.