Pregnant AUNTY or AH-MA?

I witnessed an interesting dilemma yesterday while waiting to get into our lunch-place. I was with my extended family, most notably my grandma, for some mother's day celebration thing.

My dad, brother, cousin, and I got there first, since our cabby was pretty fast. Waiting in line behind us was a pregnant woman and her husband. He was motioning for her to take a seat on this nearby bench. She was muttering something to him, probably reluctant or something because for awhile, she did not make any attempt to even go towards the bench. Perhaps she thought she should wait till the queue got shorter and they got nearer.

Along comes my grandma, with rest of the entourage, and she happily plonks herself down on the only seat left on bench, at my aunt's suggestion. My grandma is visibly aged.

Now I swear I caught the woman glaring at us after that, albeit trying to do so subtly, never so much as looking directly at me.

I wonder, what did she expect us to do? Ask the old lady to give up her seat for the pregnant woman who needed it more?

And if the same—one seat two dames in distress—happened on our MRT trains (where all commuters are caring, civic-minded, and wonderful individuals), who do you think would win the seat?