Scribe Yearling is a member of the Brotherhood of Steel. She is located in the Arlington Library, which is close to the Citadel.
If the player speaks to her nicely, she will allow you to use the terminal on her desk for the Wasteland Survival Guide quest.
She was assigned to the Arlington Library due to a disagreement with Scribe Jameson.
If the player speaks to her nicely when they first meet, you can bring a Pre-War Book to her for 100 caps and 10 experience points. You can do this for each Pre-War Book you find.