Go to green pastures disposal site and go to the left of the icon on your map, you should see the power lines from the power station close by.

You can see it and at the power lines, follow them to the right and you'll pick up a radio signal.

When you get close to the area, you pick up some rads. To get Fawkes and star paladin cross at the same time, get Fawkes from the main story line and make sure you have good karma when you come out of Ravenrock.

He will be killing enclave soldiers, get him and go to the Citadel and make him wait in the courtyard.

Go to the Great Hall in the Citadel and talk to her, be nice and when the part comes where you can ask her to join or something, say "I can't possibly stop you" and she will join.

After that there you go! You can tell her to use more ranged weapons and give her a stronger gun like the alien blaster, that will make her stronger, or the Firelance.

All you do is trade stuff and you can get it back when you trade again!