So is Shiho surprised that:

• 1. Miho is at Kuromorimine
• 2. Miho is a robot
• 3. Miho is able to sneak up next to her
• 4. All of the above

ok I'm like 99% sure the 'mob' characters standing with Erika are Revue Starlight characters.
L-R: Hikari Kagura, Karen Aijo, Claudine Saijo, Mahiru Tsuyuzaki, and Maya Tendo

cognizantmirai said:

ok I'm like 99% sure the 'mob' characters standing with Erika are Revue Starlight characters.
L-R: Hikari Kagura, Karen Aijo, Claudine Saijo, Mahiru Tsuyuzaki, and Maya Tendo

Yeah, I wasn't able to find anything concrete, but the resemblance is pretty much spot on, so I went ahead and tagged it.