I use Sindel as my secondary, and I would like to give some inputs on her strengths that people who don't play her may not understand.
- I believe if you can land some hits, you can end the combo in a variety of ways to control what you would like to do when the combo finishes (i.e. full screen for zoning, close for fly cancel pressure)
- Instant air flight fireball (builds meter for fly and fireball, plus recovers fast, can machine gun inputs when you get used to it)
Also, people always comment on how "SINDEL NEEDS ARMOUR". I agree, with armour she would be top of the mid tier (IMO). EX Step up has some on wakeup, and can use that for people who try to use that to their advantage, + gives good distance.
A lot of people think if you get them at mid range you will start zoning. This can make them attempt to move in. You can take advantage of this and rush in on them, with a mixup or a pressure string.
Her 2, 1 string and 1, 1, 1 string are both good IMO. Second hit of 2, 1 is low, I always use flight cancel after into throw or 1 1 1. 1 1 1 flight cancel is safe, (I think it's neutral on block, maybe -1 or -2).
Anyways, I believe Sindel is underrated, and if she got armour on EX Step Up (not just wakeup), she would be so much better. Because really, when you hear about Sindel, does anybody ever complain about how terrible her zoning is, or flight cancel. I think people are too hung up on armour. It is a problem, but it gives her 'E' tier status, undeserved IMO.