Letty sending the text to FBI explained
I think a lot of you are oversimplifying the whole situation too much and looking too much at the surface. There are many things driving her to do what she does.
I don't think Letty is that dumb. I think that Letty only sent the text so the FBI can track and get Javier back to her. Remember the phone call that happened where Javier was saying "goodbye" to Letty? Letty looked so empty when he said that. On top of that, she wanted to get her son back. So many things running through her mind. You can't deny that Letty feels something for Javier. There is a connection. I don't think she was ever really going to snitch on Javier, up until the phone call. She was about to lose the one thing that made her better. It was her only way of getting him back, even if it meant betrayal. That's what I think.
So instead of hating on what Letty did, which is understandable (don't get me wrong), but at least try to understand that there could be more to what the character is doing.