Yes, but this is Patsy, a horse of a different color. She didn't reckon appearances the way the average person might.
a) I guarantee you she had more than one festive emsemble for the holidays
b) a few hours is all it takes for an outfit to get unfresh - perspiration, wrinkles, cigarette smoke
c) all the more reason to change - wanting to look nice and put-together in a fresh outfit
She was going to be flying, and I tend to think she'd have wanted to wear something comfy and relaxing on the plane for the trip up, not the same outfit she wore the previous night. I don't own as many clothes as Patsy would have, and there's no way I'd dress in the same outfit I wore to a party the night before if I was planning on being on a plane for a couple of hours - especially not if I was meeting someone I wanted to look good for. She'd just end up looking wrinkled and travel-weary.
A murderer doesn't shower and change if she's run out of time, which is what I assume happened here. Maybe the clock ran out when John got up, and all she could get done after that was scream and begin the charade. She completely overlooked the pineapple, too.