Boy's mom or Dad's girlfriend?

This scene has kept on coming to my mind and I still couldn't figure out who/what exactly the role of this lady should be. Last 2 weeks while waiting for Hubby to meet potential car buyer, we went to McD so that both of kids can occupied their time on the playground. While watching them running up and down on the slides, I noticed this family of 4 sitting by the side of the playground. I were watching them for quite long and I guess the mom noticed as well. I were almost staring at her, not able to control myself.

The grandmother (i guess from the father's side), 4-5yrs boy, the father and the mother (this is a mysterious woman for me, but I guess she is the mom since the boy looks so much like her). 4 of them were having their dinner. The grandma was busy feeding  porridge to the boy. The father was scolding the boy for not eating up. The mom was sitting far at the end, eating her fries and talking to the father. She didn't even take a look at the boy. Not to mention try to feed him, she has totally no physical/verbal/emotion contact with the boy.

We were there for ~30minutes and I just can't keep my eyes away from her. She is young and pretty lady. I was wondering if she is really the mom or is the father's girlfriend. I kept on looking at her, waiting for her to do something or talk to the little boy. Is she the mom? Why she'll just let the grandma feeds the boy and she was just enjoying her meal? The grandma was feeding herself and the boy at the same time. She looked happy and not distracted although the boy was throwing tantrum of not wanting to have the food. Only the grandma and father responded to the boy. Can a mom past the responsibility to the grandma? Is there some family conflict that cause her not to interact with the son? I just couldn't find a valid reason for a mom not to take care of the son when they are together.

I guess I'm just too busy body, but I just couldn't imagine a mom in this way. If only she is the mom...