Oh wow, that's a serious bug, and I've never heard it before! So you went through the whole game up to Lamar with just Alicia? I'm sorry, that must have been annoying.
I'll replay that part of the game and see if I can find out what happened. Do you remember if the Inner Parasite battle happened? It's when Miriam rejoins and gets her powers unlocked.
Would you like a version of the game with something added to unlock Miriam's abilities? I can put something in the school for you.