This is a discussion on Fluctuating water temps - is this bad? within the Cyprinids and Atherinids forums, part of the Freshwater and Tropical Fish category; -->
I bought a thermometer recently for my tank and noticed when it put it in that the water was reading 17 degrees ...
These variations are small and happy over several hours, so it gives the fish time to adjust.
For the new tank, even though she's a goldfish, I'd pick up a heater and set it to a good temperature just so it doesn't drop so low. Fancy goldfish are more sensitive that common goldfish and actually should be at at least 20C to be comfortable.