What 'it' refers to

The protagonist, Philip moved in with his uncle Mr. Carey, the Vicar of Blackstable after his mother's death.
He goes to the medical school St. Luke's in London.
He came across his ex-girlfriend Mildred on the West End, found her being a prostitute, and she and her baby moved in with him.
They returned from going out late evening.
........................................
They reached the house, and when they got into the sitting-room Philip lit the gas.
"Is the baby all right?" he asked.
"I'll just go in and see."
When she came back it was to say that it had not stirred since she left it. It was a wonderful child. Philip held out his hand.
"Well, good-night."
[Of Human Bondage by Somerset Maugham]
I'd like to know if "it" means "what she did."
Thank you in advance for your help.