Ok reasons other than “no” -
shes 17, her face probably hasn’t finished moving and growing to what she’ll look like as an adult, leave it a couple of years for her face to settle
its normal to hate your face at 17 and want a homogeneous face to the idea of beauty that is narrowly defined at school, but in a couple of years she may love her different features.
if she has filler, when taken out it can make lips look stretched and haggered, so if she starts now, she has to go on with this for the rest of her life or end up with the mouth /upper lip of a 70 year old by the time she’s 30. This is a several hundred pounds every 6 months for the rest of her life commitment. Hold off starting that…
every young woman I know who’s started with a little bit more to look natural has ended up looking overly filled and “I’ve just had dental work” look within 5 years.
this fake lips look is beginning to wan in fashion circles, give it a couple of years and thinner natural lips will be back in fashion, as per above, if that happens she’ll find it hard to go back to a natural look. It’ll be the over plucked eyebrows of our generation, but with an added kicker of costing hundreds to keep up and not as simple as drawing on eyebrows to cover it.
All in all, I’d leave it and hope when she’s 18 she doesn’t bother herself.