What exactly does she like the most about online learning - just the lack of distractions, or also the way the content is presented?
I'd say it really depends on the person and what they're studying. Some teens really latch onto learning on screen because they can pause, rewatch, or go at their own pace. But honestly, being able to focus at home isn't the same as actually retaining stuff long-term. She could sail through an easy lesson online and then really struggle three weeks later when she has to build on it.
Going back to in-person classes can be rough precisely because she got used to an ultra-structured, quiet environment. But frankly, interacting with other people matters - it forces you to explain things, to debate, to make mistakes without consequences. Maybe the real problem isn't online vs. in-person, but rather a transition that didn't go smoothly? Trying to blend both for a while could help.