This sentence should be: Ustedes mandan cartas a su abuela cada mes.
Translation: You(formal) send letters to your grandma each month.
Ustedes- you(formal) Mandan-send Cartas- letters/cards A su- to your Abuela- grandma Cada- each Mes- month
The sentence you provided was grammatically incorrect since cortas means to cut and Mrs. is used to introduce a married woman which should have been mes which means month.
