It normally takes around 1 week or slightly more to get an answer from TK to a feedback.
Check-in staff has no authority to amend a ticket (in a voluntary rebooking situation like this). Did she talk to ticket office at EWR? Also for rebooking EWR-IST-ASB to EWR-IST only, TK CS would be looking for award availability for EWR-IST first; it is not just a matter of removing a segment as you changing the award ticket completely.
DId you try to contact the local TK ticket office to assistance/intervention?