"Well that must be nice" - sarcastic or friendly?

My mom of all people told me this one last week:

Two old bitties are having their weekly luncheon together:

“Oh Ethel, did I forget to tell you that my youngest son is now engaged?”

“Oh, isn’t that nice!”

“And last week my granddaughter won 1st prize in her gymnastics meet.”

“Oh, isn’t that nice!”

“And I can’t wait for our 50th anniversary-my husband is sure to surprise me with some expensive piece of jewelry, as is his custom.”

“Oh, isn’t that nice!”

“What was the most expensive thing that your husband has done for you, Ethel?”

"Well, let’s see…I’d have to say it was his sending me to charm school early in our marriage, so that I’d say, “Oh isn’t that nice” in casual conversation instead of “Who gives a flying fuck.”

I go with the previous poster.
People tell me stuff that has nothing of interest for me. They are happy, and proud. I am disinterested, and bored, yet, not rude. I look for something to say. “Well, maybe your son isn’t an idiot after all…just slow!” Nope. “So, the fat slob daughter finally landed a man? Great!” So, while I am casting about for something, I remember what I heard somebody else say: “Well, that must be nice!”

Best wishes,
hh

Depends, but in the OP example, I’d lean toward friendly or neutral. Unless, of course, it was followed up with “I wouldn’t know, myself. Some of us have to work for a living.” In which case I vote for snotty, sarcastic, whininess.