Or she put them there herself, getting ready to go out, then the argument developed elsewhere, she was killed by Josh, and he forgot to move/remove them.
I haven't seen the original news source for these items being on the bed, so I'll take that with a pinch of salt until someone can provide a link. However the purse and keys left anywhere in the house are another pointer to her not leaving of her own accord IMO, and a slip-up on Josh's part if he killed her or abducted her.
I wonder if, during the house clearance on Saturday, any of her friends noticed if all her coats were present. Most people only have a couple of cold-weather overcoats, and if she was already dead when she left the house I doubt Josh would have bothered to wrap her in a coat. The presence of all her coats would be a point against Josh, though the absence of one wouldn't necessarily show that she wasn't killed by him, as she might have already put it on when she was killed and it was left on her.
I'm still of the opinion that it was all sparked off by a late-night argument, not pre-meditated, Josh had to act quickly to remove her body and missed a few things, and that's why Josh's story is such a sieve.