To tell the difference between "stolen" and "robbed", take a look at the difference between what is included in the two sentences/parts of sentences.
"I've been robbed" - the focus is a person (I). The second sentence doesn't say anything about what was taken.
"She found her ring had been stolen" - the focus is on the thing that was taken. Notice that this sentence includes what was taken.
So, "PERSON" was robbed. "THING" was stolen. Of course, you can steal people too, but in that case, we usually say "kidnapped" or "abducted".