This is the second of two progress reports we have on Maggie that Will received from Miss B. McKenzie. There were surely more. The first one that we have is:
Because Maggie's mother had died in childbirth, a wet nurse was needed for Maggie. The internet tells me that baby formula was first invented in 1846, but it was a century after that before baby formula became an adequate substitute for breast feeding. Therefore a wet nurse was found, but she was from San Jose, whereas Will was in San Francisco, so Will sent Maggie with the wet nurse to San Jose, and visited when he could.
Note: Miss McKenzie was not the wet nurse; the wet nurse was an Italian woman. I think there's a mention of Miss McKenzie in a letter from Mama Margaret: