Obviously we did not see the death, but it could have occurred as early as the end of TOS's first year or as late as a day before the events of THE WRATH OF KHAN. My personal estimated guess would be between the second and third years of TOS. I thought the question could be asked, in case anyone has established the stardate time through official novels or even fan fictions.
If McGivers had bought it mere days before Chekov's visitation, I can see that making Khan extra-angry.
Honestly, from the dialog of ST:TWoK, I would assume she died BEFORE Ceti Alpha VI exploded - which was 6 months after they were marooned there. So, mid-second Season of TOS at the latest.