GoodtoBetter, as you've got the keys to the flat, you could start taking stuff over and dumping it all in one room to sort out after? (Not an easy game if it involves then having too much furniture in another room and having to move everything around like that game of sliding squares where there's only one free space!)
What I did when I moved here, as it was only a mile from my previous house, was I got friends to help me pack up portable stuff - clothes, books, kitchen stuff, DVDs, etc etc and then got the removal firm to just take the furniture.
Here you don't have a deadline to get everything out, as even your mum isn't going to sell off anything you've left after 24 Jan! But I would assume you don't want to have the conversation with her about whether you can leave some bits to pick up over the next few days. Is there anywhere else you could store stuff that you're not going to need immediately?
More importantly, you have to rest - moving house is a marathon, not a sprint.