They Are Both Right
Amelia understood that the letters they wrote never reached Amara, even her grandma informed her that Michael might do something like hiding the letters from Amara, when she saw how hopeful her granddaughter was and how eagerly she was waiting for a call or a letter.
Bria knew her brother very well and seeing Amelia hopeful every day and getting disappointed after not receiving a letter or a call, she decided to tell her the harsh truth.
In spite of knowing that Michael would hide letters, Bria could not help and send a few letters to Amara as she too had a slight hope that someday Amara might get those letters and she would change her mind about being the leader of the Russo gang.
With all this information and experience of getting disappointed, Amelia did not have a very good impression of Michael.
She did not visit Italy to attend his birthday but took it as an opportunity to meet Amara and celebrate Christmas with her.