Well how about tying flat on her back, making sure as best you can that she can't even wiggle, say again with a cocoon of tape and tights, butttt leaving small gaps in it here and there, especially in ticklish/sensitive areas like the middle of the back, backs of the knees, etc. to put ice in and be able to tickle even more intensely, but because of the cocoon there's no hope of release until whatever time you choose!

Also add gag knotted as also added before, but I recommend that you Don't use any form of stuffing because when you're young, and especially being tickled, there's a high risk of choking. And even with a knotted tights gag, at the first sign of even slight unease to breathing by it, remove it. Always play safe!!

And then you could add a blindfold with tights, and then put some tape over the tights over her eyes, just to ensure she can't see, and finish by covering her ears so she can't hear either, which, with all those senses numbed, will make her so many times more responsive to the tickling as her sense of feel should probably increase with the others decreased
