I have been asking that all along. David Jimenez hd some contact in Istanbul, whether through his church or on his own, as he arranged the lodging for him and Steven through " friends of a friend," if reported correctly.
Also, as I mentioned yesterday, if SS didn't send the text to her sister, who did? It must have been someone who spoke perfect colloquial English and knew she was " coming home tomorrow...YAY!" Apart from T and the landlord, who knew that? Certainly not Z, who couldn't have written that in English to begin with. Either SS was alive at 4:20 pm Turkish time when that message was sent, or someone with perfect English and knowledge of her plans the next day wrote it.
I'm beginning to think there may be some connection to the landlord. I agree, the way things should go is the landlord writes in his native language and LE gets an official translator (and even then it might not be perfect colloquial English).
I do agree that 'YAY' is not only colloquial but contemporary american 'slang': but what I find a tiny bit odd is that it sounds more like somebody going home after a tiresome summer camp, than somebody going home after a 'once in a lifetime' dream vacation.
In reading (way back now) a 'timeline' of SS perambulations in Istambul, I did get a distinct impression of something others have speculated about: a sense of wandering around, or aimlessness, and possibly it was as others have suggested a lack of contacts.
Mentioning which, the Turkish accommodations for the family members were probably not made public because of privacy concerns.
Just my 2c worth.