Reyes' main job is to listen and write down the reports she get from the communications radio. She is rather bright as even with some believable reports, she has the sense to have the Courier investigate outrageous reports and also make new codes for all of the communication devices at the Ranger camps.
After you finish the quest "Return to Sender", you can inform Reyes about what happened. If you select the dialogue option, "Forget about it. It's over." She will respond by saying, "Oh, well thanks for helping us get to the bottom of this, I guess". But she will not say this vocally, as the audio file is missing.
"We've received some disturbing reports from some of the Ranger stations - heavy casualties at Alpha, Super Mutant Legionaries at Delta. The weirdest one has to be the Great Khans and their trained Deathclaws at Foxtrot. These reports can't be accurate. Can they?"
A number of interactions between the player and Reyes were cut prior to the release of the game. Of the more interesting options which were cut, a partially removed dialogue option exists where the Courier can tell Reyes "But I already got a tattoo with your name on it. Want to see it?" The circumstances which would have led to the Courier saying this to Reyes are not explained.
Reyes is also an alcoholic, and is, as a result, not taken very seriously by the officers or troopers in the camp.