A topless photo would let me know whether her tits are the right size and shape for tying.
Personally, I'm fond of standing ties that allow the sub some movement. They're helpless, but you get to see their reactions better than in totally restrictive bondage.
Feet spread a shoulder-width or a little more apart and tied to the floor. Rope or a tight strap about her waist, tied to anchors on the floor in front of and behind her. Set it up so that she can't quite straighten her legs, tiring them rapidly.
Beneath her, a well-supported vibrator, such as a Hitachi Magic Wand. If she pushes upwards with her legs, she is barely touching it. If she rests her tiring legs, she's flat against it.
Arms bound at the elbows to her sides so that she can't reach much of anything of importance. Not that it'd stop her from trying, I do like seeing struggling. Her hair might just be long enough to tie to a rope anchored above her. If not, I'm sure I could come up with some other way to keep her upright and resting on that vibrator.
I'd continue by teasing her for a while. Keep the vibrator on low, and alternate between running ice cubes over her body and dripping candle wax. Approach, but not quite reach her nipples, and push her to beg for it.
She'd probably find her first five or ten minutes at this quite pleasant.
As her sensitive, overstimulated pussy is forced to cum again and again, and her tired legs can no longer keep her off the vibrator, I'd shift more into torturing her.
First, she'd be cleaned of the wax. Cold water helps it break off nicely. Then I'd apply electrodes to her breasts. I like a position right next to the nipples. The sub feels it in the nipples, but you can still reach them for play. She'd get a brief reprieve from the vibrator as I insert electrodes. A bipolar electrode in her pussy will be connected to the same TENS unit as her tits. A second bipolar electrode will be inserted in her ass, and connected to a muscle stimulator, forcing her to clench over and over.
A bit of bare-hand spanking and tit-slapping at this point would be nice. Mostly, we'll just sit back and watch as she struggles, listen as she begs.
As you and I begin to grow bored, we'll give her the controls to the electric. "Turn it up. Show us what a good painslut you are. Show us how much you can take. Then we'll think about letting you off the vibrator."
She turns the knobs, and pushes her boundaries. We take back the controls as she struggles.
We let her stew for a few more minutes. I caress and spank her ass alternatingly. You kiss her and whisper words of encouragement as she starts to sob.
We turn off the vibrator and begin to untie her from the anchor points. The electric remains on, and her arms are still tied to her sides. We turn off the electrode in her pussy and remove it. We lay her down on a bed, and you fuck her as the electrode in her ass continues to make her clench on you. You pound her swollen, over-sensitive pussy.
I cum on her tits as you cum in her. We turn off the electric and untie her. Gatorade is pressed into her hands and we begin to massage her, making sure she's ready for the next round.