@Disposable Aunt: I am so sorry. This is awfully hurtful, unnecessarily so. You're worthy of being thought of, and, if not invited, at least told the truth directly. Your sister may have thought she was doing the kind thing by keeping most of this information from you, but as we're seeing, intention and impact are not the same.
You don't need to explain why you're taking a break. Take the space you need to process this, to grieve it, and to talk to people you love and trust about what's going on. It's important that you keep hearing the true message that this is not about who you are or how you show up in social situations. I know that you've done a lot of work in your life to navigate being neurodivergent in a society that isn't accommodating or understanding. Try to get back to a place of remembering that the work you've done is important because it helps you, not because it helps others tolerate you. You're enough.
At a certain point, it will be useful to talk with your sister about how this situation affected you. Take the time you need to gather your thoughts and feelings on this. She won't be able to undo what's done, but it's important that you're heard.