A Mystery Solved

For weeks now I haven't been able to figure out why two firecracker plants in the planter out front are thriving and the third is dying. Last night we came home to this:
Actually, when we first got there she was lying directly on the plant. She sat up when she saw us, but since she was sitting right in the middle of the plant it didn't help much. And then, since every good nap requires a luxurious stretch and kneading of the paws...
You can't really tell in the photo, but she's still right on top of the plant. I no longer have to wonder what is killing that one particular plant and nothing else. However, now I have to wonder what I can do about it. Would barbed wire look trashy?