I don't think the best explanation for this set of facts is that the woman suddenly got the urge to take photos outside of her usual setting and that her killing is random, unrelated to her online contact with unknown men and the subsequent pattern of behavior she exhibited on the basis of this contact. An aspiring drug runner perhaps?
Here are the salient peaks in 'Explanation Space,' the realm of possible explanations for what has occurred. The peaks differ in their handling of the two embedded propositions of the above paragraph (the clauses following the 'that' tokens).
(i) Affirm both propositions: the woman really did just decide to travel overseas for the first time to take pictures, and her killing really was unrelated to her contact/interactions with the unknown men.
(ii) Deny one proposition, affirm the other v1: The woman did not just decide to travel overseas for the first time to take pictures, but rather did so for an unknown reason. However, her killing was unrelated to her contact/interactions with the unknown men.
(iii) Deny one proposition, affirm the other v2: The woman really did just decide to travel overseas for the first time to take pictures, but her killing was somehow related to her contact/interactions with the unknown men.
(iv) Deny both propositions: The woman did not just decide to travel overseas for the first time to take pictures, but rather did so for an unknown reason, and her killing was somehow related to her contact/interactions with the unknown men.
(v) Wiggs-Falconian analysis: Aliens/the USG/the Illuminati did it.
Given the basic-most facts understood thus far, (iv) seems to me the most likely option. It seems to imply either that she was a drug runner or was otherwise involved in crime and that she was killed on this basis, or that she was there not to take pictures but to have a tryst or some other under-the-radar interaction with the man in Istanbul, and that he killed her. Which we opt for ought to be determined by her background, what investigators find on her cellphones, the content of her online interactions with the unknown men, and the their backgrounds.