To me the fact that your daughter has OCD and ADD is irrelevant. Your daughter (youngest) was watching TV and your oldest disrespected her by changing the channel and since your youngest doesn't watch TV this was probably a treat she was looking forward to and instead of letting your youngest watch TV and talk to your oldest about respect she punished her.
She the yelling and screaming was a overreaction, but when you looking forward to something and have someone take it from you, your not going to be happy and calm about it.
My advice to you is stop letting your oldest disrespect you and her sister and she needs to move out soon since she doesn't seem to like rules.
Also stop punishing your youngest for your oldest behavior