My dd1 doesn't have autism but has learning disabilities and can be difficult to manage in large groups.
As her parent I know what she, and I, can manage. Some parties we accept. Others we don't.
Luckily I have friends who realise I am capable of making this decision and who accept dd1 for who she is.
Don't invite your 'friend' (note that I use the term loosely) if you don't want to but do it in the full knowledge that it is because you can't deal with her son's autism or her, very understandable, feelings and reactions to it. It is so that you don't feel uncomfortable. Please don't kid yourself otherwise.