As far as gear,
ShadowC only shows ~80 dps of optimizations. Seems like she pretty well knows what she's doing there, but it stinks of AskMrRobot. I would swap to ShadowC for the best results.
Others have pointed out the problems in her rotation. The most helpful thing is going to be getting a buff/debuff tracking addon. Most use WeakAuras (and you can find good imports; zero work). I use IceHUD because it looks pretty. Track CDs, CPs, SnD, and RvS.
From there, it's really simple:
- Use CDs on CD
- Keep SnD up
- Keep RvS up
- SS to 5 CP
- Evisc
There's a bit more to it than that, but before you start messing with Anticipation, Insight, Rupture, or anything else, she needs to get the basics down and be able to execute them.
Also, Assassination is a probably easier. It moves a lot slower and there's less to track.
Icy-Veins' class guides are really good.