you might want to ask your mom for a clarification: are you expected to entertain these girls the whole time? or just put in an appearance and meet them?
also ask what she knows about their interests. You never know, there might be something in common. (for instance, contrary to popular belief, girls DO play video games)
Having an intense stim session before they arrive will help you not need to stim as much during the gathering. Pick some socially acceptable stims for during the gathering. If you involuntarily stim anyway, and it's commented on, use it as a teaching moment - that it's a reaction to stress, and even positive stress is still stress..
Very likely, the two girls will entertain each other with chatter and you will only need to feign attention, if that.
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If it don't come easy . . . .
. . . .hack it until it works right
Aspie score: 142/200 NT score: 64/200
AQ Score: 42
BAP: 109 aloof, 94 rigid and 85 pragmatic