It's because she's not married yet in spite of her age, at least in Naruto Shippuden.
I don't know about her marital status in Boruto.
Edit:
For the downvoters, it'sIt's very common in many Asian cultures thanthat an unmarried woman would be angry if somebody mentionmentioned something related to marriage, especially when she's about 28 and up y.o. It's like if you ask "how much do you weigh?" to a woman.
I don't know about her marital status in Boruto.