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's very common in many Asian cultures than an unmarried woman would be angry if somebody mention 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.