We've visited Roatan in late November / early December many, many times over the years (but I have only been a certified diver for the last four). The weather conditions at that time of year are a total dice roll. It is right in the middle of the rainy season - not that it necessarily rains hard every day (although it certainly can!), but just depending on how much rain Roatan gets before and during your visit it can have quite an impact on visibility due to runoff from the island since the dive sites are all so close to shore. Some years we have had great weather around US Thanksgiving, and some years it has been absolutely horrible.
Also at that time of year Roatan can be impacted by "northers" that make conditions in West Bay/West End/Sandy Bay difficult or nearly impossible to dive. Many operations in those areas have arrangements to dive on the south side when that happens, but in many cases they don't do three dives in the day during a norther because the logistics just don't work.
I too read a huge variety of recommendations about wetsuits for Roatan. It's hard to know what to recommend partly because everyone's tolerance for cold differs so much. Your daughter probably won't need much if really any but the thing is that if she does start to get chilled on say the third dive of the third day you won't have a lot of options for getting her something there. I don't recall seeing a lot of selection for child-sized wetsuits in the very few places on the island that sell scuba gear. Since it is her first scuba trip I think you would not want her to get chilled partway through, not be able to get her a wetsuit to help overcome the cold, and have her totally turned off of diving because of that bad experience. I would recommend getting her something inexpensive before your trip (especially since she will outgrow it quickly) that you could possibly unload later in an online marketplace.
Last year during the first week of December the water temps were 82-84F every day. Actually a few days last December the water was warmer than the air temperature and I was ever so glad to get back into the water after a (to me, at least) chilly surface interval. I use a 3mm shorty over a long-sleeve rashguard for thermal and exposure protection, and much prefer it over just rashguard and swim shorts. But I'm not 10 years old and I am acclimatized to the tropics, so it's probably not too helpful of a comparison... I also have a cheap rain shell that I picked up at a Target in the States to wear to and from the dive sites and during the surface interval.
Roatan is easy warm water tropical reef boat diving, and even when the weather is uncooperative we have immensely enjoyed all of our dive trips there.