Even although Ally is quite outgoing, the first day in our new house she spent hiding behing the washing machine

It took her a couple of days to relax and settle in. I suppose if your cat is more shy than usual, it may take a bit longer than that! I would assume the best thing would be for the cat to be reassured by your presence - spending time with her as you have already been doing. I'm sure she will settle in - it will just take a bit of time and patience. Good luck!