No, not at all, she hasnt damaged herself. In fact, it is quite normal to masterbate in the way you described, and i imagine quite common. Grinding the pubic bone causes a pressure stimulated response around the clitoral area. (sorry i cant be more scientific!)
Im incredibly pleased about how attentive you are to her needs, good for you!
The trembling, intense feeling you described is also quite common...im speaking from experience - its a cross between pleasure and pain. Id suggest lowering the intensity of whatever youre doing, whether it be a case of kissing / rubbing AROUND the clitoris instead of directly ON it? Or maybe be a little softer in whatever youre doing?
I would highly recommend suggesting to your girlfriend, as long as you think she wont be offended, to use a sex toy in her own time..so that she can work out what feels good for her. A rampent rabbit would be perfect as she can alternate between clitorial and / or vaginal stimulation, and she will be able to lower and increase the intensity too. That is what i did anyway...ive have never been able to reach orgasm through intercourse alone, and i imagine the same applies for many women. Its just a case of every woman being different. The only way i can reach orgasm is to use a vibrator during sex, and i wouldnt have realised that if i hadnt have experimented with sex toys!!
It isnt anything that you are doing wrong, and i love that you both communicate with each other. Best of luck and keep up the attentiveness!!!