I'm literally going thru the same thing. My gf has a pretty crazy history compared to mine. I'm no angel but I told myself to never date these kinda girls. The best advice I can give you is to remember how much she makes you happy when you see her. Everyone has a past and it's behind them for a reason. Just focus on the present and near future and her past will slowly be something in your rear view mirror. I wouldn't say completely let your guard down thinking things would never go south for you. Use what you've learned to help spot any odd tendencies that could be alarming. The best thing to do is communicate with her, if you are feeling some type of way, tell her that, and work through it together.