@Ubi-Woofer Okay, so... After countless reloads of previous saves, meditating and fast travelling etc all of which didn't help the interaction to appear at the corpse after the latest patch 1.1.1, I believe I have found the problem.

It could be a possible workaround or something that the team could pinpoint and help a bunch of people out.

Back in November I came across Cordelia and she was majorly over powered for me, so rather than attempting it multiple times or letting her kill me, I ran away. As fast as I could. I didn't however expect her to chase after me outside of her bog, and she chased me across East Anglia. I got caught up in a number of enemies and I managed to slip away using stealth.

Tonight (Jan 14th), as I was exploring East Anglia I unexpectedly heard the battle music and her health bar appear in a solid gold colour, randomly in the middle of the woods. To my surprise, she was in fact still stood where I'd managed to escape her two months earlier. She didn't attack me, she was completely stationary, and I couldn't kill her either.

I thought of something crazy, so I started hitting her with my spear and pushing her in the direction of her bog. I can't remember the name, but there's a swampy bandit camp not too far. South West of her bog. I found her near there. I pushed her all the way back to her bog and as soon as she entered into the circle, her animation began and I was able to start the fight and ultimately kill her and get the dagger.

Oddly, she must have been stuck in the exact location I left her, even after all the patches since November, after travelling back and forth between Norway and Vinland and after me completing the whole story and putting about 200hrs in. It's a bizarre one, but the fact I couldn't interact with the corpse was because she was out there this whole time, in the open world. Waiting. For me. Hope this helped somewhat.