I do feel a little silly for asking about this, but here we go...

So, about one month ago we adopted a little kitten, she is now 3months and a bit old. Been having her inside for the most part with some occasional walks outside to get her used to being outside, as she is an outdoor breed and will eventually be allowed to walk freely in or out. For as long as she is for now indoors, we've gotten her used to using the litter box, one of them with a small hatch to get inside, which she is good at using. BUT, whenever she decides to to curl one down, it f*cking reeks, it smells quite bad. I've had other cats before and none of them have smelt like this... Obviously we get rid of the shit asap, but then also clean her with a wet cloth so that she run around smelling equally bad and to teach her to was herself.

We're not feeding her anything unusual, she mainly eats this dry food(which was quite expensive) https://www.specific-diets.co.uk/cat/everyday-diets/kitten-fpd-gb. Furthermore, we're using some silicon cat sand, as that was what we got recommended.

Edit: Forgot to add an essential part to this!

This is the litterbox in use;

She tries to dig her shit down, but instead of digging it down into the sand or put sand over it, shes just scratching the sides of the cat litter box. Also after going out of the litter box, shes wiping her paws on the floor. But yeah, the scratching of the box inside is very loud and doesnt seem normal either. Is the box too small for her? Or could this be related to the sand of choice?

So, anyone got any tips or tricks here? Is this normal-ish? Obviously shit smells... but this seems almost out of the ordinary... Does the type of cat sand matter a lot?