If you Google "pine oil" in regards to it's toxicity to rabbits you will find blogs on how it's toxic for rabbits. However, one must understand that "pine oil" or in these cases pine essential oil is extremely concentrated and diffusing pine essential oil vs. having an actual pine tree in your living room are two VERY different things. Pine forests are actually part of a wild rabbits habitat and they will often nibble on young pines especially in the winter months. I grew up on a 150 acre farm with over 100 acres of it being forest and wild rabbits could almost always be found in the pine groves. They really seemed to love hiding in the brush from fallen pines. I also use to raise rabbits as a kid and every year we had a live tree (many different coniferous species including pine over the years) with no issues. The biggest concern with a live tree is if it was sprayed with pesticide or an artificial scent and your rabbit was able to nibble on it, but since your rabbit will be far enough away that shouldn't be an issue.