Yeah, I know I'm a guy but this post begs a reply. There are devices designed for this purpose called "dilators"(for us lay people these are expensive dildos). They are actually designed for post-hysterectomy therapy. An otherwise healthy woman should have no need to "stretch" her vagina as there are many more entertaining ways to go about this. Anxiety is more likely the culprit here but you need to give us a little more info to go on. I do know, for a fact, that pregnancy will take care this.
to thghten you can do keegal(sp) exersises. this is told to preg. women to tome there muscles for birth and pushing and to get back to normal after birth. All you do is clench your vaginal muscles (like stopping your urine flow but not while your peeing) just for a few min a day can do a great deal for tightening.
Actually I used the Kegal exercises when I got pregnant and they worked wonderfully. Neither my husband nor I have noticed any difference in sex since having the baby, actually it is tighter. Also during labor when I was pushing it made it alot easier. They are really easy to do. Pretty much it is just tightening the muscles that would make you stop peeing. There are some web sites you can look up to get more information. But I have not heard of exercises that stretch