Developing an OC

I've had this girl stuck in my head for awhile and I never get a chance to develop her in any of my other RP's

Her name is Marilyn Moran and she is Sebastian's younger half sister. Just turned 18 she is curvy but lean, long auburn hair that has dark brown streaks through out, and midnight blue eyes that slant down on the inside corner. Sebastian doesn't know about her and she was adopted by Irene Adler at a young age after he mother passed away and was raised to one day take over the business. She ran away right before her eighteenth birthday because she didn't want to be in that life. She is living off the streets of London trying to find anyone that will take her in and help her get on her feet.

I'm looking for any feedback as well as a possible story line.
THanks in advance.

Marilyn Moran is an awesome name!

Thanks I've changed her story quite a bit since this post actually.

Yeah? What's the backstory now then?

Marilyn is twenty-three, and the best counterfeiter in London, She runs a business from her flat, but mostly her business comes from one James Moriarty. The look is the same, tall and lithe, long red hair streaked through with dark brown, Sebastian knows who she is and she has watched the destructive relationship between her brother and the criminal in silence because she needs the money that Jim pays her for her work.

Oooh, I like it.

Thanks I really appreciate that!! I just wish I could come up with a good storyline to put her into you know.

If Marilyn objects to her brother associating with Moriarty then maybe she could eventually turn against him and go to Sherlock for help, wanting to set Moriarty up and get Sebastian away from him for good. Sherlock would overlook the fact that she's a criminal herself because he's so keen to get to Moriarty.

I like that idea actually.