Sounds just like me a few months ago...
For me, it's pretty hard to make me cry from just spanking alone, although there are a couple of implements that get me close. Have you tried a cane? The looped cane has a particularly nasty sting. The Lexan is good, lots of sting and not much bruising. You are right, a wet bottom stings a lot more, so does no warm-up.
The guys are right though... you need to find her trigger point -- what makes her lose control. I've discussed this with a bunch of people and it's different for everyone. You will have to get into her mind somehow... that is the key.
Some need to feel that it is a discipline spanking ... or actually BE one if you can pull it off in your relationship. Verbal build-up, anticipation, fear, disappointment... ya need to find out her weakness. Try tying her down or put her in an uncomfortable position. Even though I can be very stoic and can be totally still... when I am tied down, I don't have the choice anymore and it definitely trips my emotional trigger.
Good luck, crying can be a very free-ing feeling and Lancisto is right on... make sure you are available for aftercare. If she is not used to feeling that vulnerable, when she does get to the point of actually crying, she may feel out of her element and somewhat uncomfortable with the situation.
Sammie