Silent Darrow is probably the strangest/most messed up thing she's experienced, but doubles/clones come very close. And werewolves.

Grantaire misses the sort of air of Paris, the unique culture specific to Parisians, and also just the friends that aren't in Darrow. Joly, Bossuet, Bahorel, Feuilly etc. I would say Enjolras but "miss" is sort of not quite the right word for Enjolras, though he does miss him.