Any stories I've heard of Queen's the past week is that even if the person is one grade away, they didn't get in (AAB/ABB).
I doubt it was because of your learning difficulties. If you met the required grades then they would have accepted you, if not then they have every right to deny anyone who didn't fulfill the requirements. I have no idea the requirements Queen's had (In terms of an Access Course) for Drama but if you didn't meet those requirements, doesn't it make sense that's why you weren't accepted? Not discrimination?