I wanted to find that article before I responded to you, but like I said it read about 10 years ago and not having much luck finding it.

But yes wetnurses were available to all women because not all women can produce breast milk.

If one poor woman's baby is starving it was not uncommon for a friend or sister to fulfill that role to help them. Women were pregnant more frequently due to no birthcontrol. So a woman lactating was more common. However they weren't hiring a wet nurse in the same way the wealthy were, and if a poor woman could feed her baby she would. A rich woman(almost) always hired a wet nurse regardless of her ability to produce milk.