The quest can start in two different ways by speaking to the lady herself or by finding what she has lost.(You are more likely to find her first though!)
As I say its a very simple quest but does introduce you to a new character who has links with two vanilla Fallout 3 characters. I won't tell you where you can find her, don't worry she is in a place you will visit more than once and pretty early on I would think. There will be enemies to face , unless you have already been to the location and cleared them out. The place she sends you isn't somewhere involved in another quest so unless you were just exploring I think you will discover this character before ever being in the location. Its a fun place to be aswell!
UPDATE
I've now actually managed to solve the no chat after the quest problem for those who have downloaded this before.
Fixed: Quest trigger being missed by fast travelling.
Version 3
Added some lines to Amata's dialogue options during "Escape" where she mentions Ariana. If you start this mod on an existing save the players options will suggest that he/she already knew of Ariana. If you start from scratch you will get the Amata dialogue options.
I'm looking to increase her chat options for after you have completed the quest but please try version 3.0 and endorse if you can. Its my first real mod so support would be nice
Thanks
Update 3.1 - Fixed wrong message if you already have the item when you meet Ariana
VERSION 4.0 (Bug Fixes)
Made the file an esm for a better head and body match. Also given added a Race just for her to avoid conflicts
NEW
I have added another Ariana download, its this quest but if you have RR Companions Vault mod added (in the mirrors) you can then have her as a companion
http://www.fallout3nexus.com/downloads/file.php?id=11276