I spoke to my wife about this, as I do about all things of interest or concern, and as I consider her to be something of an expert on orgasms (special thanks to me
), this is what we have come up with together ......
This type of orgasm, for many women (not all) can be far more intense than a clitoral orgasm and thusly, in most cases, be a simple matter of similar yet differing intense sensations. There are SOME women who simply cannot enjoy this type of stimulation / sensation / orgasm as the feeling of it is simply too intense, or in some instances, it is simply being done too harsh or rigorous.
My advice is to talk to her about it in a nonsexual setting and get her input on the subject BEFORE attempting this again. Then, with her consent, use the same technique you have before, only go slower and use a lighter touch. If your efforts yields the same results, it is most likely she is in the minority of women who simply are unable to enjoy this sort of stimulation.
We both LOVED the rope trick and had a good laugh about that, but in all sincerity, your fears of her anger at that prospect is not an unreasonable concern. So you should consider fine-tuning your technique first, and add the rope later .. trust me when I say this, it truly enhances the experience.