5 years ago, my sons were 13 and 16 and we took them to Belize that year. They still talk about it. They had the time of their lives. We stayed at DuPlooy's on the mainland in the rain forest. They swam in the river, canoed, hiked, explored Mayan ruins. We took a day trip to Tikal in Guatamala. The young college aged guide was FABULOUS. He took them on an "off the beaten path adventure" through the park. We then went to San Padro. They played soccer with the local boys, snorkeled, danced, fished, swam with the rays and sharks at Shark Ray alley. She will have the time of her life. You'll be exhausted, but it will be an experience you'll never forget.