Disheartened that the beloved Camp Wawanakwa where she spent her childhood was turned into a radioactive dump during Revenge of the Island, Ireland had been so obsessed with wanting to do her part to restore the campsite to its former glory.
After Revenge of the Island ended, and after the radioactive ooze was cleaned up, Ireland participated in a community replanting of trees that had previously been torn down due to "Chris' meddling with Mother Earth". She also volunteered to help anyone whose life Chris endangered, whether it was contestants, or interns, or anyone else involved with ROTI.
Ireland knew that nature-lovers like Bridgette and Dawn had not made it far in the Total Drama series before, so she decided to change that by signing up! And since she knows Chris likes drama, she decided to pack all-green clothes and dye her hair green just so she can get noticed! (Of course, the dye she uses is organic.)