My opinion would be to shorten that category name. These categories "art journaling" "journaling and related art" "ATCs" could well be separate categories which would function differently for readers to find your blog.
To make your own decision, look at what the tags bring up when you do a wp tag search:
http://en.wordpress.com/tag/art-journaling/ vs http://en.wordpress.com/tag/atcs-art-journaling-and-related-artwork
One shows lots of folk talking about art journaling, while the other shows only you talking about "art-journaling-and-related-artwork"
Also watch your stats for which terms people search to find you. This info is more interesting than the raw stats about how many hits you get. (In my opinion)
Besides attracting readers, your categories help you to organize your own blog, and if you need the long title for that purpose, then maybe you could use abbreviations.