You might be wondering whether a vagina can be stretched, the way a man's penis is enlarged when it gets stiff. It is not a myth, but it is actually true. If a girl thinks that she is too tight for most men, then she should get longer foreplays, or more lubrication, or she can also start doing Kegel exercises.
Since a man has an erection during a foreplay sooner or later, a woman needs some foreplay, as well. Just like a blowjob can please a man, an oral treat can make wonders to a woman, as well. Unfortunately, women with a tight vagina need a lot more time for a foreplay than an average man would. It does not matter how tight a woman originally is, a sensual foreplay will give her enough time to let a huge penis penetrate it, and she can even enjoy it more.
If she had some kind of trauma in the past, like a rape or abuse, then you will need to see a professional, though, since there is no foreplay that can lubricate and stretch her vagina. A professional can cease the blocks in her mind, so she will be able to not only let you inside her body, but also to reach an orgasm in the end.
Kegel exercises are a special workout for pelvic muscles. They can help her to be aware of her own body, so she can tighten and stretch her privates willingly. She should start with intermittent urination to know which muscles to use, then she needs to constrict them two or three times a day for a few minutes.
You can be sure that one of these techniques will lead to a better sex life in the end.