According to what Serena the witch told the siblings, Perdita was currently in Marco's room urging him to rest.
"Don't you find what she said amiss?" Marco asked when he grew tired of telling Perdita he didn't need to lie down to rest.
Perdita was busy arranging and keeping things in the room in order even though the maids had done the job in the morning. She was just doing it to keep herself occupied and not think of Marco's health situation.
She stopped and turned to look at Marco who still sat on the bed. She responded to Marco's question, "I do find what she said to be confusing," A thoughtful look now on her face, and before Marco could open his mouth to speak, she added, "But what can we do about it? The king said she is the only one that can help us heal you. So you have to comply with whatever she said."
