If its not unjured please take it back to where your sister found it, DO NOT release it into a pond, at this time of year they will be looking for somewhere to hibernate, rock piles or thick grassy banks where they can find somewhere to sit out the winter. It will have left its pond, could be in someones back garden as they prefer still water, to find somewhere to hibernate.
All newts are a protected species and you could get into trouble from the RSPCA for holding a wild animal. Sounds daft but I know someone that got a real ticking off for putting a swan in their garage as it wasnt injured (just stunned)!
Hope this helps.