I'm learning more and more from these threads that the majority of people don't use her correctly. She is a zoning character, which means you need to play keep away and use projectiles. The only time I rushdown or abort that plan is if the opponent can teleport. I quickly become a defensive/reaction player. Meaning I punish there mistakes with her combos. If you leave the 3 out of your combo you can still knock them into the air. sooooo........jip,b3f2,yell,jip,b3f2,dash,b12,dash,111,hair whip. 44% easily. Another problem with Sindel players is that they constantly go for this combo which is a huge mistake. You will be punished repeatedly. I'd stick to her easier combos. Here's a few.
1.jip,12,hair whip.
2.b12,yell,b12,111,hair whip or cartwheel.
3.b12,yell,311
4.b12,dash,b12,dash,f12,hair whip or cartwheel
5.b12,dash,b12,311
Those are basic, but really easy to use. I would stick with those until your opponent learns to respect b1 and uses crouching block. At that point I would start using b3f2.