ROFL, I don't think Mamori would just transform though. In the anime, Mirei would say "Fusion Trans/ Liberate Arms" before Mamori Drives and I think the students could do it without the words is because they are practiced enough without it.
^^It could also be - and I hope not - just practice to Chinatsu and Akari can't say no and is also deeply hurt by it. That's why she's crying. TT_TT I really hope this is not true...