Somebody from the Dollhouse-world just let me Summer is staying on Dollhouse as a reoccuring. As we originally announced a month or so ago to the interwebs, she was signed to just two episodes then.
Summer is currently in episodes 5 and 6 (production order).
Alexis Denisof has filmed episodes 1, 3, 5 and 6 so far (production order), FOX tells Dollverse.
Minor update: episode 7 started filming today, Summer isn’t in it this one. But she’s back later in the season, never fear.