One thing about me is perfect, and it's my teeth. Yeah, I couldn't be naturally thin and athletic or have great skin. Nope, my one big perk had to be something that is expensive but fixable and moderately invisible to other people. I'd definitely trade my excellent teeth for perfect eyesight. Regardless, it's genetics. I was fortunate enough to be born with strong teeth and can't claim that my perfect teeth are a result of any action beyond simple brushing.
In contrast, my 19 year old takes excellent care of her teeth, but she rarely experiences a cavity-free check up. She inherited a mouth full of Swiss cheese teeth from her Daddy. Her needs are greater than mine, and I should investigate buying her one of these Sonic Care tooth brushes. Since I am still paying her health care costs while she's in college, it might be a money saver for me . . . But better health for her would be the real benefit.
You might suggest that your daughter look into xylitol gum or mints (or swishing a bit of xylitol dissolved in water around a few times a day if you want the budget approach, but I'm lazy, so I just suck on a few mints per day). The tl;dr is across innumerable, careful studies, regular exposure of your teeth to xylitol (3-6x per day) reduces dental caries by about 30%, or more. The modern view of cavities is closer to infection management, and xylitol helps reduce the ability of the bacteria that causes the cavities to breed and/or stick to your teeth.
On the OP topic: My dentist force-converted me to an electric toothbrush. Not because of plaque - I was doing fine - but because of some gum recession. AFAICT, it's been effective -- she's stopped making as many worried sounds. When I researched it, the most typical view from the studies was that an electric is no more effective than a well-trained human doing a proper job of brushing with a manual toothrbush, but the (good) electric toothbrushes are a bit more foolproof to technique errors.
Costco sells the replacement heads, or you can amazon subscribe & save them, to save a bit of the cost.