Hey, MiniChan. Sorry to hear you're going through this. I don't know if you have a therapist, but if you don't you should consider one that specializes and/or has been trained in trauma therapy. There are no meds that will "take away" PTSD-- it doesn't work that way. The meds may allow you to sleep, or make you less anxious, or make you less depressed, but they cannot "fix" or treat the core issue, which is the trauma.
When I first went on meds, my psychiatrist told me point blank: since you have PTSD, the meds will help you with about 40% or maybe even 60% of your symptms, but the only way to work through PTSD itself is through therapy. In my experience, if you address one PTSD symptom with medication then it's only a matter of time before you get a new and different symptom. The point is, until you deal with the actual trauma itself, the symptoms will continue popping-up.
Try not to feel guilty about feelings of confusion when it comes to your sister.
Best,
racha