Hi, SlimJim87:
I can provide one point of view from "the other side" (I'm 50 and have gone through my share of heartbreaks).
Why did she do it? Because if she's as super rich as you say she is, very little holds any value for her. Including people and their feelings. She probably sees you as little more than a pebble on a beach, one out of many to be picked up, carried along for awhile, then skipped into the water to see how many times you'll bounce.
I was lucky--in my first breakup I got everything I gave back (it wasn't much but it was priceless to me). That could be because I was there when he broke it off. All totaled it probably wasn't worth more than a few bucks (this was back in 1980) but it meant everything in the world to me.
Why in heaven's name would you give her something after you broke up? You didn't save the receipt? You certainly could have returned it to the store and gotten a credit to use at some time in the future.
People can be extremely heartless and I'm sorry you were victimized by one so uncaring. Mourn your loss (when you look back after awhile you'll see that it was waaay more her loss than yours) and move on with your life. There are some questions that will never be answered and many of them have to do with relationships.
Good luck and do keep posting.