Do a forum search and check out the Diet and Nutrition Section, particularly Lys Charts (
http://www.guineapigcages.com/forum/...arts-info.html ) and you will find an answer.
I surfed through Lys Charts and checked out the sticky on forages to see if I could feed the girls mint just this morning. I could only find stuff on spearmint and lemon mint, not normal mint, so I did a forum search and got an answer.