Here are my opinions.
Bad Matchups-
Smoke 3.5-6.5 - its not too bad if you respect his shake, you can sometimes fool him though, and punish it. But his pressure is really something else, sindel really has no answer to his teleport pressure,.
Jade- 4-6 - Green flash, nuff said.
Noob- 3-7 - OMG, for me, it is horrible. any air fireballs will be punished by a teleport, he can trade with you, idk, i just dont like this matchup. sindels a great zoner, but noobs zoning + teleport makes this so much harder.
Raiden- 4-6 - His teleport shuts any type of zoning down, his pressure isn't too bad, but the fact you cannot zone limits sindel.
Kung Lao- 4-6 - Not as bad as it seems, but tough. Can trade a few projectiles, plus bait his teleport. Deadly pressure, dive kick moves him in, not too hard, but difficult nonetheless.
Sektor- 4.5-5.5 - His projectiles are a little hard to deal with, but can be overcome, his teleport shuts down youre zoning, and his homing missle forces you to stay grounded.
Mileena, Lui Kang, Kitana, were all meant to be bad MU's, but imo, they are 5-5. I've been doing very well against Mils and Kits, i need some more exp tho. IMO
Mileena vs Sindel- 5-5 - DO NOT JUMP- Respect her teleport. all you have to do is, stand block, and naked crouch as a sai passes you (or ex sai), then quickly stand block and repeat. punish all teleports, and rolls with 3 scream into combo, time your low fireballs right so it may go under her sai, trade carefully, DO NOT JUMP. it isnt too bad. Use 1 scream as an AA for a jumping mileena.
Lui kang- 5-5 can trade pretty well with him, bait out flying kicks and bicycle kicks to punish, his pressure is IMMENSE, but sindel can zone him pretty well
Kitana- 5-5 this one is a bit tougher, but can be done. Her fans are scarier, as are her jump kicks, but she has no teleport like mileena. low fireball her ground fans, zone her out carefully. back up and do scream to punish a square boost, or let the square boost pass you and quickly to hair grab before she lands.
Sonya, Subzero, and Jax are tossups
Sonya- Sindel controls the zoning VERY well. but once she's in or youre in the corner, it's deadly to you. You can't really AA her due to her Dive kick. (i want to say 5-5, but due to sonya's rushdown,) 4.5-5.5
Sub zero- Baiting out slides, and zoning him is nice, but if he's in, it can cause trouble. It is DEVASTATING when you're put in the corner (again, i want to say 5-5, but due to his corner pressure) 4.5-5.5
Jax, I'm kind of iffy on him, he can be zoned decently, but you push yourself to the corner, also, his lunge punch can cause problems. That i know of,, sindel does not have a small hitbox, so his pressure is immense. 4-6
Kabal- Sindel controls the zoning, but forces him to come in to her, which is a recipe for disaster, since she has no armor or fast startups 4-6