Meng Jie said.

I feel that buying words is more intimate than sending words. Buying words for others feels like you are a family, and sending words is generally used between relatives and friends. Which word you want to use depends on how close you are. When you call her Sister Meng, do you call her after everyone or alone? If you are the only one who calls it that, it means that your relationship is better than others. You can use the word buy. (and to popularize a knowledge for you, any word you use has nothing to do with the word humble, which is a bit puzzling)