Hi ukseniorlady.
Sorry to hear that the last collectable in your game is being so elusive! I want to reassure you that there is no glitch in the game. I just checked mine from "way back when" and all the collections are complete in 2 of my games, 2 others almost complete, and apparently I forgot to pause the 5th game so that tribe has been lost!
Other players have also posted in the VV2 Forum that they completed their collections as well.
Here is one such post.
Perhaps installing one of the available collections mods will help? One that makes that one elusive pebble stand out from the others? Which pebble is it?
Another idea is to install a mod that has all the collectables invisible except for the one you're missing. Since you've been playing the game for so long you probably don't need the points you'd miss from the other collectables being invisible.
Is that something you'd be interested in?
I'm sorry the lack of a reply has been so frustrating for you. Is it possible you've been posting on some other web site for assistance? The last post from you here concerning VV2 was over 3 years ago and was answered by LadyCFII the very same day. To see your posts, click on your username in any of your previous posts and click "View posts" from the menu. You can also click "My Stuff" from the menu bar and then click "My Posts."
I truly hope you find this reply helpful.