As a workaround you can select your image in the gallery app (picasa folder) and choose "Edit". With that you have the option to edit the image in PS Touch.
This workaround doesn't work for me. When I select edit of a picasa image in the gallery app, I do not get any options...it only lets me edit them with the tabet's internal editing system.
Is there anything else I can do or try?
Thank you for your help!
The only other way I can think of is to save your picasa image to the local gallery of your device and start from there or copy&paste the image to blank PSTouch document with the same image dimensions
Hope that helps.