yes is possible load data from a different source, like a database sqlite the database used by Ubuntu touch (Ubports)
For an example about chart + data loaded from sqlite database look at this:
("Database access with QML" and "QML and Charts" chapters)
The sample App associated with "QML and Charts" chapter can be found here:
(is the project named: WeatherRecorderChart)
NOTE: that project are made with old Ubuntu sdk - ide But should work also with clickable (just 'clickable desktop' in the folder with the .pro file)
In case of does not work with clickable, the source code of the sample App is valid you can use it.
the two file you are interested are:
'ChartUtils.js' is the file containing the query to load data from sqlite database and prepare the data-set for the chart
'ChartPage.qml' is the qml page where the chart is drawn
To load data from a Libre Office sheet...sorry but i don't know how to do (maybe someone here have an idea, solution).