If she wants to avoid the wait, then get she can get a bus from the Belize City bus terminal (commonly known as Novelo’s) located on West Collet Canal.
The bus companies authorized to operate on the highway in the Northern Zone are NTSL, Belize Bus Owners Cooperative (BBOC), Chell, Gilharry, Russell, Tillett, T-Line and Venus. Northbound buses depart from Belize City about every half hour beginning at 5:30 am; last departure at 7:30 pm. Most are Regular buses, but there are a few Express buses throughout the day. Some buses continue to Chetumal, but if not, then simply change in Corozal to a bus going to Chetumal. I was told that the last departure from Corozal to Chetumal is 8pm, but some information shown on the schedule posted on the wall of the terminal differs from information received directly from a Corozal bus terminal supervisor.
A Regular bus from Belize City to Corozal is about 2.5 hours & BZ$9.00. An express is faster and a few $ more. The bus from Corozal to Chetumal is almost an hour; that's not because of distance, but it can take a while for a bus load of people to get through customs/immigration.
In Chetumal, buses arrive at Nuevo Mercado (about 1 km from the ADO terminal).
The Belizean buses are used Bluebird school buses; most of them are not very comfortable, not air-conditioned and are not well equipped to handle luggage, but they are cheap! The Express stops for passengers at Orange Walk and Corozal. The Regular stops anywhere along the route.
Check the NTSL website for updates:http://www.nationaltransportbelize.com/schedule/district/?d=3
Have a look at the site I set up for bus travel:http://belizebus.wordpress.com/