Amin & Kyle mused about why Dany dropped her ring when being sorrounded by the khalasar. They seemed to think that the ring was most likely from her wedding to Hizdhar. I strongly disagree. The ring she dropped was given to her by Khal Drogo. The reason she dropped it is that if she were to be recognized as a Khaleesi whose Khal has died, she will be shipped off to Vaes Dothrak to join the Doth Khaleen; no questions asked. She needs to hide her identity as a Khaleesi in order to have even a sliver of a chance of talking her way out of this situation.

Now, to be fair, if the show follows the books in this regard, it won't matter since the khalasar that finds her is headed up by Khal Jhaqo (a former blood rider to Khal Drogo) so she'll be recognized anyway. As far as she knows at the time she is sorrounded, however, it's just a random khalasar.