Needs these mods to work:

RR Companions Vault by NosRhyfelwr
http://fallout3nexus.com/downloads/file.php?id=3644

Sharing and Caring Companions by ZableBlaze
http://fallout3nexus.com/downloads/file.php?id=2399
Download the SCC master and the "Talk to Anyone" feature.

Fallout Script Extender (FOSE)
fose.silverlock.org
For SCC to work.

UPDATE: Ive looked at the comments and I noticed that people can't initiate dialogue with Robyn. So, I looked into what had been inconveniencing people and here's what I found: I could only initiate dialogue with her because I was using this mod in conjunction with another Companion mod: ZableBlaze's Sharing and Caring Companions. That, along with an additional SCC feature called Talk to Anyone, is the only way I know of to initiate dialogue with Robyn.

So, it seems that in order to get this mod to work properly, one would need to install Sharing and Caring Companions and the Talk To Anyone feature in addition to RR Companions Vault. Also note that SCC needs FOSE to work as well.

My first mod. Using the RR Companions Vault tutorial, I made this little girl companion.

Little Sister Robyn can be found in the apartments section of Vault 1. She awaits for someone to take her on great adventures across the Wasteland!

She comes equipped with a Railway Rifle, 10mm Pistol, stimpacks and tons of rail spikes and bullets. She should be wearing the outfit Zip from Lamplight wears, but without the helmet.

Robyn shouldn't be too hard to miss; after all, she's probably the littlest kid in the vault...

Oh, also please post screenshots of the adventures you take her on! Please provide some feedback and report any bugs to me.

Thanks To:
NosRhyfelwr for creating RR Companions Vault and the RR Companion Tutorial

ZableBlaze for Sharing and Caring Companions

The FOSE crew: ianpatt, behippo, and scruggsywuggsy for FOSE

DK3 and toadlet for pointing out the problem

toadlet for posting the screenshot

Bethesda for a really fun game!