OK, seems like I completely misunderstood your intentions in my earlier post, but I wasn't the only one...
The way I understand now, you're looking for trust exercises - not discipline - to find limits and expand on them. If it was difficult to think of corrective discipline for someone you do not know, thinking of excercises in trust for them is nearly impossible.
You need to know about boundaries of a person before you can even start to think of stretching them. What they all have in common though, is taking an area which is important to your sub and asking for control over it. It could be as simple as cutting her hair (if you're any good, of course...), but your piercing example also fits the bill. These both give you control over her body, for which a lot of trust is needed.
You need to identify the area's in which you wish to expand. Should she have trouble with intimacy, maybe have a nice, romantic dinner together with her blindfolded, where you just feed her lovingly. If there are any toys/kinds of pain she is afraid of, you could slowly start to use those in play, trying to make it feel good. Make sure you are always prepared for anything when stretching limits, by the way. You need to show that you are in control at all times.
This of course works the other way around also. If she knows something to be really important to you, you can show trust by allowing her control over it. This kind of exchange reinforces bonds between people. Be careful though, if anything goes wrong it goes wrong badly.
I hope now at least I understood your question.![]()