Oh man, I've done so much of this matchup. And yes, it is truly ass-tastic. He'll use Nirvana as a shield for him to approach, and she will stop all lobelias and pumpkins. If you want to try lobelias for zoning, I recommend the jump A ones, as the angle is good and so is the startup/recovery.
The most important thing for this match is positioning. Run around, plant some seeds, get some friends out. Be patient, be tactical. You do NOT want to get caught between the two. And if you do, well, time to practice your blocking. CA if you have it, really. Even worse though is being caught in the corner. You could end up spending the entire match in there. Keep a careful eye on the positions of everything on the stage.
Also, if you do get Carl away from Nirvana, don't be reckless when attacking him. He can do good damage on his own, and even summon her in the middle of his combo for some pain or sandwiching. For example, if you airdash or wind-airdash over Nirvana to an isolated Carl, he'll probably just 6A you on the way in for a good 3K or more damage, depending on where the doll is.
And yes, oddly, the frog is one of Rachel's best tools in this fight. He'll slide right through Nirvana, which stops Carl's human-shield technique. And when George is going off, Carl can't move or use Nirvana, so that's your chance to move in to try to get some damage, and to drag him away from her.
Oh yeah, and trying to shut Nirvana down is fairly useless. It takes a lot of effort, she recovers health fast, and he can still fight well without her. However, if you feel like smacking her around now and then, I don't blame you.