The path you have posted does not seem to work. During new theme adding I have enter path like this:
It seems OK but later, when I try to set this theme for template, I get DirectoryNotFoundException, and error like this:
"Could not find a part of path: 'C:\Projects\sitefinity4_test\Sitefinity\Template\~App_Data\Sitefinity\WebsiteTemplates\DefaultTemplate
It seems that sitefinity is looking for theme in ~/Sitefinity/Templates instead of ~/App_Data/Sitefinity/WebsiteTemplates.
And it is not interpreting "~"