Goodness me , I feel for you. However give her time , a week is not long so early days . We got our rescue three years ago , she was only young though and was extremely nervous, racing to round the house, hiding when we approached , I was beginning to think ' we hat have I done!' She also refused to use her litter tray! Fortunately it was in the utility room on a tiled floor , she always ' went' close to her tray - fortunately! Although you are providing her with the litter she has been familiar with why not try a change, I buy the compressed sawdust litter. Also have you placed her tray well away from her food bowl? - that is important. Failing that a check over at the vet may be the best move. I hasten to add that our cat is now the biggest softie ever , a real lap cat ! She took at least 6 months to settle with us. Good luck .