In your shoes I'd actually complain. I understand what the benefits are for the SCD child, but that child is not your concern.
My reasoning being that she needs MAXIMUM exposure to NT peer group, outside the home, as a direct result of being the younger sibling of a child on the spectrum in order to best facillitate her own social development.
She's only 4 and that's a critical age for NT social communication development, and your family life has experienced significant disruptions what with the fight for your DS, the move, a new baby and all. I just think you have to prioritise her welfare over other people's children at this delicate stage.
I'd feel very differently if Star's family had a different history. There are 28 other NT children in the class that can help the child with SCD, most of whom would gain a lot of long term benefit from learning about difference at this age, having had no prior exposure iyswim.
Sorry if that sounds harsh, and I really don't want to offend anyone on this forum.