Hi Amy,
I went through something very similar. I was around 10 or 11. I buried my memory for about 25 years so you are way ahead of where I was. You're going to have to treat the addiction and the PTSD at the same time. One works against the other. They are both equally important. The anti-depressant medications are non addictive. Effexor and Paxil can be very hard to stop taking, but the other SSRI's are fairly easy to stop taking. They can give you enough relief to learn some new coping methods.
I've heard concerns from others who have addictions that the medication can be a trigger for them to start using again so it is an individual decision. I've tried most of the anti-depressants and with most of them you can't even tell you are taking anything. They help you sleep and take the edge off of the anxiety.
Keep posting and keep talking. I'm glad you're working with a therapist. That will really speed up your recovery.
Hugs,
MG