Let's number the characters and let you decide

"Ha! This happened with my(1) mother-in-law(2)! She(2) wanted to be called grandma, but when my(1) daughter(3) was a baby and first learning to talk, she(3) pointed to my wife(4) and said, "Mama!" and then she(3) pointed to my mother-in-law(2) and said, "Momo!" She's(2) been Momo ever since."

I interpret characters 2 and 4 as women, 1 as a man (assuming this because there is no mention of adoption), and 3 as a female child.

So not counting the baby, 2 women, unless (1) is a woman.

There are. My mother-in-law, my wife and my daughter.