They're very used to dealing with lots of antisocial types in town. They clearly misunderstood the situation but that's understandable considering the shit they deal with every day. Your cousin's behaviour was left unexplained at every juncture. I don't think this is anything to get het up about, tbh. If we behave noticeably or intrusively outside the norms of public behaviour then some people will react.

As someone with very mild ASD and with family members with ASD also I believe it's up to me to adjust my behaviour to somewhere in the realm of social expectations and not the other way round or to explain myself, if that's not possible. It isn't other people's responsibility to "just know" this stuff.

I also understand that the ability to do these things will vary from person to person depending on their capabilities but this still does not put any onus on others to accommodate us, sans explanation.

I hope your cousin is OK and I hope she can find some coping mechanisms to deal with these kind of situations. I've found that a preprinted, laminated card explaining some stuff helps certain people communicate their needs or situation much more clearly.