Structure doesn’t just have to mean “do XX watts for XX minutes XX times” but it also applies on a more macro scale of how many hard days/week and how many easy and progressive overload (whether that is duration or power). So even if she won’t be motivated by the intervals in TR, maybe she would do better with just riding around Zwift and then doing 1-2 Zwift races per week to get some intensity.
My GF started riding the trainer back in the spring and while the thought of just riding and starting at TR would probably make her want to shove a brake lever in her eye she likes the progression and the focused work. So she does the TR workout, with a movie playing with subtitles, also with upbeat pop music in her headphones.
I know my first and second paragraphs say two different things but the point is that no one here can probably give you the right thing for her but rather it might be one, the other, or a combination. Maybe start on Zwift and then move to TR. Maybe she needs Zwift races to really push herself. etc. But
I’d say that depends on her level of training going in. If she is a true beginner then almost anything will be beneficial. And the most beneficial thing would be to keep it fun.