She's a non-resident on a working holiday visa, but has a SIN and received a T4.
Her residency status is important when filing for her first tax return with the CRA. Once that is established, she would move forward with filling out her T4.
Foreign income earned prior to arriving in Canada. We want to know about your World Income (Foreign & Cdn). It boils down to whether she will get a full year or is it prorated from your date of entry.
She will not be taxed twice on her income from home, under the tax treaty Canada has with Austria, as it is taxed at source, she would file for Foreign Tax Credit on the income from Austria.
To access the FTC form, go to the "Find" icon at the top right corner of your screen and type in "Foreign Tax Credit".
Please take note that as a non-resident, first time filing a tax return with the CRA, she will have to print and mail her return. She will not be able to Netfile.