Yes, pixel art assets can be scaled up as long as you keep the proportions intact. In Photoshop you should activate the "nearest neighbor" option when scaling them 300% (to reach 48x48), or you can use some other software like Aseprite.
I can scale them, but it takes some time, which is why I usually just provide 16x16 and 32x32 versions. I'll see if I have some spare time to add 48x48 versions to my packs these days.