Will my mom need to check in at the counters for her international flight after a domestic flight in Thailand?

Hello! My mom and I booked a domestic flight from Phuket to BKK, then she has a separate international flight to go back to her country. She's not checking a bag, so will she need to check in at the counters in front and go back through security? Or can she just go to her gate? How much time do you think she needs?

I'm asking all this because the domestic airline changed our flight from HKT to a later one and now there is only 1.5 hours between flights. I've already contacted the airline about switching to an earlier flight and I'm waiting to hear back.