So I will need to find existing data of outcome of art therapy with survivors of abuse and trauma. I do not have a clue where to begin or how to find the data.
If you are looking for published research on art therapy outcomes with persons who have experienced trauma, you may also want to consider Ebsco Host, PsychINFO, or PubMed.
Google Scholar/Ebsco Host/PsychINFO/PubMed will return papers, not data. However, once you identify the papers of interest, you may want to write to the authors and ask if they can give you access to the data. Sometimes you will be able to see that the authors used secondary data. You can then try to get access to that data too. Finally, go to https://www.icpsr.umich.edu/icpsrweb/ University of Michigan provides access to multiple datasets. Check if they have what you need. Good luck :)
I suggest you to assess some psychological outcomes, like stress level, coping abilities, and emotions management. Clinical outcomes as depression and anxiety, and maybe you can use some psychopathological scale.