Hi Theresa, are you able to successfully test QueryPropertyHistory service, i.e. before using it in the chart widget? If the properties are successfully being logged in that valueStream yes you should just be able to query it via the QueryPropertyHistory.
As a general check I'd always test the service from within the Thing in case if properties are not coming up at all or if i am getting error while using that Entity in the Mashup.
So, there is a Thing and a ValueStream is assigned to that Thing. Could you please confirm if you are running the QueryPropertyHistory Service from the Thing.
Also, have you selected the Mashup On Load while adding the Service in the Mashup so that the data is available for TimeSeries Chart on Mashup Load.