Hmm, if I can, can I sign up as a canon character, since I have had some ideas? By the end of it, she will still fit in with the Theives guild quest line. Actually they work well with it.
Light Armour, Archery, Sneak, One-Handed, Pickpocket, Lockpicking, Alchemy
Thieves guild armour, Nightingale Armour, Nightingale Bow, Nightingale Blade, Various Arrows, Steel dagger, Various potions and poisons.
Never stays in one place too long
Nightingale, Thieves guild (Ex: Theives guild believes she killed their leader and want her dead)
Karliah is mysterious to say the least, yet somewhat honest. She will tell the truth, but conceal what she wants to. She was less of a pessimist before the death of her lover, Gallus. Since then she has been more of a pessimist. She is motivated to get revenge on the person who ruined her life, Mercery Frey, going to extreme lengths like purchasing Goldenglow Estate and funding Blackbriar Meadery. She wishes for him to receive the same treatment she did, to be hated and hunted by the people she called friends.
(Things in bold are different to the game)
Karliah is the daughter of Dralsi Indoril, and a descendant of Drayven Indoril, Queen Barenziah and possible the Dunmer saint Indoril Nerevar. She was trained in the art of thievery by her mother, and became part of the thieves guild in Riften. Here she met Gallus and Eclipse, whom she became friends with.
After Gallus deemed her worthy to be a Nightingale, he took her to Nightingale hall, where she was inducted as a Nightingale, an Agent of Nocturnal.
One night, Gallus was told that Nocturnal wished to speak with him and Karliah. She snuck out of the ragged Flagon cistern, meeting Gallus near the entrance to Nightingale Hall. Little did she know that Eclipse had seen her sneaking out, and followed her, worried she had gotten into trouble. When her and Gallus spoke with Nocturnal, she revealed that Karliah was followed, and revealed the presence of Eclipse. Nocturnal deemed Eclipse worthy to be a Nightingale, based on the fact that Eclipse stalked Karliah and Gallus and entered Nightingale hall undetected.
A year after Eclipse joined the Nightingales, they heard word of someone in Whiterun publishing a book called Nightingales: Fact or Fiction, revealing their secrets. Eclipse offered to take care of the situation and left for three weeks. In their time alone together, Karliah and Gallus grew closer than ever, to the point where they fell in love. When Eclipse returned, he walked in on her and Gallus sharing a kiss. Eclipse grabbed his posession and left. Karliah never knew why. She didn't see him again until a year later.
In the next year, Mercer Frey, another member of the thieves guild was inducted as a Nightingale. A year after Eclipse disappeared, Mercer heard word of a corpse being found at Snow Veil Sanctum, wearing Nightingale armour. Fearing that their presence in Skyrim may be revealed, Mercer and Gallus left immediately to go to Snowveil Sanctum.
Two weeks later, Mercer returned. He entered Nightingale HQ with his sword drawn, covered in blood. Karliah never saw him coming. When she finally did notice him, her bow and dagger where out of reach. She was at his mercy. Mercer admitted to killing Gallus, then charged at her, with intent to kill.
Karliah thought she would be dead within a few seconds. Suddenly Eclipse appeared in front of her, and they were surrounded by a circle of flames. Eclipse shot Mercer in the wrist with his bow, and then fought off Mercer with his daggers, stabbing him in the stomach. Mercer fled, and before Karliah could ask Eclipse where he went or why, he was gone too.
Karliah grabbed her bow, and made her way to the Ragged Flagon Cistern, to tell them of Mercer's betrayal. However when she got there, she was attacked by the people she once called friends. Mercer got there first and had blamed his wounds on Karliah, accusing her of killing Gallus. She was forced to flee.
Intending to get revenge on Mercer Frey, Karliah bought the Goldenglow estate and funded the Blackbriar meadery, leaving one of her connections with a message. If Mercer were to find them, to let him know that she is waiting for him, Where the End began.
She is currently travelling north through Skyrim, near Windhelm, on her way to Snow Veil Sanctum, waiting for the day when she can get revenge on Mercer Frey.
Actual character from Skyrim. During the RP she will still have the same role that she does in the game.