"I think the little dog is very pretty."
Here's a breakdown:
* je pense que: I think that
* le petit chien: the little dog
* tres jolie: very pretty
The phrase is grammatically correct but could be slightly improved by adding an article before "tres jolie," like "très jolie la". This would make the sentence more natural-sounding and complete.
So, a more refined version would be: "Je pense que le petit chien est très jolie" or "Je pense que le petit chien est très jolie la".