Ahem, now that's out the way, we can begin, we've not made much fuss about her, so our last post about the Irish fightclub queen is how to become best friends with her (female) or romance her (male).
First of all, unlocking her. Find her at an raider base in The Combat Zone (not far from Diamond City) and kill all the raiders inside. Once you've done that, go down to the cage and speak to the Ghoul inside, who informs you Cait is now useless to him. Agree to take her contract and get her to follow you.
During your travels with her be selfish, rude in conversation, pick as many locks as you can, drink and use psycho to gain her trust. Keep talking to her constantly until she triggers a conversation with you. Act nicely toward her and she'll open up more each time. You'll beed to do this three times.
The third time, she'll ask a favour, she's addicted to Psycho and wants help from you to wein her off it. There's a Vault (Vault 95) that was designed to cure people of dependencies. Now it's a stronghold of Assaultrons and raiders. Fight through them all and find the experimental chair for Cait to try, convince her to sit in the chair. Once she's cured this isn't the end however. Continue how you were before, only this time, you can't use any chems but stimpacks.
After a while, she'll trigger an conversation. This conversation is your romance conversation (you need a high level of Charisma to succeed). Choose the best friend option, if romance is red and the achievement for affinity will unlock. This also unlocks the perk Trigger Rush which lets your AP regenerate quicker while under 25% health.
Enjoy your perk, Vaultdweller.