Crazed,
I feel like you are future tripping about your relationship with your step daughter. The effects of all the time you spent with her haven't just disappeared. It is totally possible that in a few years, when she is independent of her parents and all the crap with your ex has settled down,
she will seek you out again. It would not surprise me if you were invited to her college graduation and/ or wedding.
She's been through a lot lately. Being forced to move in with her dad because her mom got arrested and is now in rehab, is really heavy sh1t. If her dad didn't want you at the graduation, I find it totally normal she went along with what he wanted. It isn't a relection on you or your relationship with her in the least. She's in as much pain over your exagf as you are, if not more. She might not have even given a thought to who came, or even really cared.