Julia did say her cell phone batteries were dead, though.

I do think Erica's alive. . .Julia is going to be tormented by the fact she killed someone because of her resentment toward her mother and that no one will ever realize it was murder. (I frankly thought it was just a "death gasp" until it went on too long.)

She said her cell phone batteries died "hours ago". She was at the triage over 24 hours I think.

Besides someone mentioning Julia's cell phone being dead, the mother didn't seem too concerned about the situation, maybe having no idea to think Julia was looking for her (just like Julia was dumb enough to be 100% sure her mother took the earlier flight). Or, if you want to add more to the characters than the writers sometimes bother to do, maybe she was letting Julia sweat it out after their fight.

I didn't catch the cell phone mention, but to me that screams of the writers wanting you to know she doesn't have contact with outside information (Matt, her mother).