Rescheduling Issue

Hi! I'm just switching over to Acuity scheduling. I have a client that booked an appointment on Saturday and wanted to reschedule from 1 pm to 2 pm, but when she went to reschedule, it showed only 2:30 pm as available. She switched to 2:30pm and asked about moving to 2:00 pm. I tried to reschedule it, but 2:00pm isn't showing up even though if she moved her appointment, it should be available. I know I can go in and manually override it to move it, but I'd rather my clients were just able to move it themselves. Is there a solution to this? The only time I have blocked off ahead of it is a few hours ahead and there's no reason it shouldn't be showing as open.

Details if they matter: Appointment is 90 minutes, 15 min block at the end. No block at the beginning. Nothing in my settings would prevent scheduling another appointment at a different time. I have it integrated with my Google Calendar.