YA, girl visits aunt (& uncle?) by ocean, makes sand city

This ought to be easy...I know I'll smack myself in the forehead as soon as someone tells me the answer. This is a young (like tween) YA book I read in the early '90s, though it's probably a bit older. A tween girl is sent to live with her aunt (and uncle, I think) on the beach for the summer. She builds a whole city in the sand, with seashells as architectural features. I think at the end it gets destroyed, but I'm not sure. I remember the cover being very pale pinks and purples and beiges.

Worldcat shows me The Village by the Sea by Paula Fox, which contains the elements you mentioned. Amazon's cover image matches, too.

That's it! Thank you so much! I tried searching for "city" and "town" and "castle", but I didn't think of "village". D'oh!

I think my search terms were "beach" and "aunt" or something like that, and I limited it to post-1980 juvenile fiction.

Glad I could help!