I would stage some interaction,
I would always make sure that she knows when someone is coming,
I suggest when she is calm talk to her, ask her how she thinks she should behave when visitors arrive, let her articulate the acceptable behaviour, help her come up with a plan, ask her if she has any ideas how to keep her brother calm, even if her ideas are wack -a- doodle, talk them through, let her spot the flaws, take your time, spread the conversation out,
ask her what does she think the guest might like, what will they need,
ask her if she could help you entertain some guests,ask her if she would like to help host, tell her if she gets really good at it she will be able to invite a special guest and choose a menu,
get her to help make some food, cheese straws and cake, and make a special table,
when the pre warned guests arrive, ask her if she wants you to help answer the door, if she manages it, great, ignore anything else,
the more she rehearses in her mind before the actual situation, the less it will make her fizz pop, repeat until it becomes a calm thing,
During each encounter praise any positives, and afterwards ask her which she bits she thought were best and which she thought were worst,
Secretly pre warn guests if they could only when she is calm ask her about the food, and ask her to show them the loo, and ask her if she could show them the garden, and ask if she could show them a picture, and totally ignore her when she is wild.
but only give her attention when she is being calm.
lots of pre chats when someone is coming, ask her what she would like to do for the guests to make them feel comfortable,
if she has something to focus on and has had lots of rehearsal time, she will be able to feel more prepared for interaction,
help her find positive way to channel the energy.
Is she really intelligent?