We will be in Belize in 5 weeks, also to dive. I do so much research before booking. Trip Advisor is a great place to ask around about anything from hotels, dive ops, and things to do. There is nothing more trust worthy than looking up reviews people have written about the things you want to do and the places you want to go and which people to trust to take you there. We will be diving with Reef Adventures. I read pages and pages of great reviews from people who have gone diving with this operator. I have read that depth limitations are an issue with most dive ops regardless of the certification levels of the divers. It's a business to them. Read up on some reviews and that should guide you and your daughter in the right direction.
We just returned from Ambergris Caye on Saturday (our first time to Belize) and dived with Reef Adventures. Ched, Ruben, and Chuckie are really great people and their biggest concern is safety, IMO. We had Ruben (DM) most of the dives and he was great about pointing out critters, doing air checks, and seemed to keep everyone above 85 feet. I would highly recommend Reef Adventures.
We chose not to do the Blue Hole on this trip because we had prepaid for our five days of dives and the first day we were to dive (Sunday) ended up being stormy and no boats were going out. So we dove Mon-Fri so we didn't lose the $$$ that we prepaid. We checked on diving the BH and the atolls that you get to go to (it's a 3-dive day out there) and it was going to cost each of us around $360. This included continental breakfast, the trip out to the BH and the park fee, the three dives, taxes, and the trip back to AC. We would have been going with Amigos-del-Mar. To go on the dive, you need to be at the boat dock at 5:30 AM and they leave around 6 PM. We did talk to one of the ladies that did take the trip and see loved it. She did enjoy diving the BH but loved the wall dives the most. We decided if we go back to Belize we'll stay out at Turneffe Island so we are close to the walls and have access to diving we didn't have around AC.