The reporting, albeit unconfirmed (as are most things in this case) of the 'tidy' apartment perplexes me.
JY didn't go to Sheffield so that she could tidy the place up and prepare for the party. No doubt she would want the place looking amazing as it was their first party in that apartment I believe.
If the bf did it on Friday evening then went on his journey he would be cutting it a bit fine with his alibi timings. Yes he could get away with a bit of extra time accounting for the slight snowfall and the busy roads, but there might be an element of doubt cast upon him by the LE, so the time of her disappearance would need to be seen as being Saturday, imo, or as late after his departure from home as possible.
The person, imo, who had the most credible reason for wanting to remove the body would be the bf. In the case of it being him, he would almost certainly have wanted it to appear as though she had NOT died on Friday, but a bit later, even Saturday - when he was certain to have an alibi, imo.
In a bid to distance himself time-wise from Bristol and the time of death, he would have to leave immediately afterwards on Friday and travel fast.
No phone call on Friday night, to say he'd arrived safely, because she was dead and in no position to answer, and this would mean that he would have to tell the LE later that she was 'missing' from as early as Friday evening, bringing her disappearance and his alibi closer together time-wise. This was too risky, hence no phone call to her Friday night.
Leaving the handbag, mobile phone, coat, keys, etc. would make it appear as though she was 'taken'. In any case, removing the phone could not be risked as triangulation would have established exactly when she went out of no.44. - again bringing closer together the time of death and an alibi.
The body dumped somewhere either Friday evening in panic (or Sunday evening in the 4 hours), now wearing different clothing - tracksuit for example as she had changed immediately when she had got home on Friday.
Apartment tidied up Sunday evening would make it look as though she had worked on it Friday evening and Saturday am (and not died Friday evening around 9pm).
Body moved just before Christmas Day to a very obvious place, as it needed to be found to show the change of clothing to make the LE think that it was not a Friday night thing.
I think the lost sock was a red herring to encourage the perp to return to the first site of disposal to check for it. The suspected perp of course being followed by the LE.
The problem of the pizza: Leaving an uncooked pizza (that she clearly bought for her Friday supper) would show the LE that she had no time to have cooked the pizza before being murdered, therefore time of death close to 9pm Friday. Cooking the pizza before the LE arrived on Sunday night was not an option as the smell would have stuck around. Pizza and packaging had to disappear.
Big 'spanner in the works' when the LL said he saw people in the grounds - this reinforced a Friday evening scenario, then the scream, however this all helps it look like an abduction thus diverting interest elsewhere.
I think the LE might be doing some things right by putting info out like the interest in the Clifton Bridge route (to make the perp feel like he'd fooled the LE with his 'clever' route), the missing sock (to make the perp think the LE were looking for a 'trophy' killer), etc.
I think we will see an arrest shortly. Softly softly.....
jmo.