What does Dedé do with Lío’s letter to Minerva? Why?9

Alone, Dede decides not to tell Minerva that Lio is hiding in the backseat of Papa's car. She goes into her bedroom and opens the letter Lio asked her to deliver to Minerva. In it, he invites her to go into exile with him. Dede decides that she will not expose her sister to that danger, so she burns the letter in the lamp.