Managed to get past this issue eventually after tips from a Reddit post:

https://www.reddit.com/r/ubisoft/comments/jrtvpi/found_a_bug_in_ac_valhalla/gga53ti/?context=3

From /u/ksa4ever70

OK I found a final solution to valka stopping at the top of the hill. This took me 3 hours of searching and trying.
You should travel to Norway and back to England for the woman (forgot her name, sigurds wife) to appear on top of the hill, then you have to push the woman down the hill using your horse (as if you go away from her she will start walking to the longhouse), after you push her a couple of meters down the hill, you need to go pick up valkas crate and run ASAP to the blacksmith to stop the woman from moving. After you escort valka to the hill she will talk with the woman and you can finish this cursed quest.

My follow up with some extra details

Confirming this approach also worked for me, life saver /u/ksa4ever70
To be more explicit on what i did, as my initial attempt to travel to Norway didn't seem to move Randvi
Go to norway (In world map there's an atlas link for those that haven't done it before)
Select a totally unrelated quest as your current tracked quest
Save the game in norway
quit and restart
Rejoin, travel back to England, Randvi was then standing where Valka normally freezes
Get on your horse and keep slowly walking at her on it from the top side of the hill slowly pushing her down, i went around half way
Sprint to Valka on the horse, jump off, grab the boxes, and come back to blacksmith, I found if I let Randvi's white square for the other quest disappear is when she would start walking back after a failed attempt.
So keep your eye on Randvi's square while Valka talks to the blacksmith, as long as it doesn't move, your good it seems.
If you cant see the white square, keep running back and forth a bit to keep the blacksmith convo going while refreshing whatever Randvi's walking timeout is

Im stuck in the same spot now, i built her hut and she still wont walk past the top of the hill, and I have Randvi in the state I can't talk to here? I don't have a save game before this state to go back to..