I've been told many times that it's in the very tip of her foot, yet sometimes, it still doesn't connect.
Is it somewhere else? Or is it actually located there, and I need to practice landing it? Thanks!
The sweetspot is more like...the center of her actual foot. Basically the center of the glowing part. Keep in mind the sweetspot is also only active for one frame.
For practice you could just go into training mode and repeatedly LK the standing AI. This will help you learn the timing and hitbox placement. Then you can "graduate" to moving characters, aerial targets, small characters, and dodge punishes (my fav).
Sometimes I'll just dedicate like 15 minutes or so in Training to landing sweetspots. And if I really feel like having fun, I'll go into FG with the tag "MeleeZelda" and only use Kicks and Dsmash.
If you don't feel like practicing that much, don't worry. Her sweetspots naturally come as you use her more. Good luck!