There is a lot of superstition and misinformation regarding the vaginal muscles during and after giving birth. Let's talk about that.
Diet controls the strength of all muscles, internal and structural. A diet that is high in protein will result in stronger muscle tone, where a diet high in carbs, especially flour products, will result in flabby and loose muscle. So increasing protein will help maintain strength.
Care given during the birth to prevent a tear will help leave the muscle integrity strong. Any muscle that is torn will not be as strong as a muscle that has been left intact, even if sutured then the muscle has scar tissue. So working with a care provider who is more concerned with preventing a tear is better than one who is proud of the perfect stitches after a tear.
Next, there are exercises, called Kegels, where a woman tightens the vaginal muscles and holds it in order to keep those muscles strong. I know this is controversial, but I am opposed to a woman doing those during pregnancy but in favor of them being done after the birth. Here is why: During pregnancy the primary hormone is progesterone, which is a precursor to Relaxin. Relaxin's job is to relax the muscles during pregnancy to prevent the baby from being pushed out of the uterus. It also allows the hips to spread, to allow for growing baby, and the vaginal tract to soften and become pliable so that when the baby is born, naturally, then the muscle can stretch around baby without tearing the vagina. So during pregnancy the job of the muscles is to stay soft and elastic, more so during the last few weeks of pregnancy. Just before baby is born the hormones change and the primary hormone is estrogen which helps with contractions, brings in milk and also starts to tighten structural muscles. After the birth the estrogen also helps tighten up the vaginal tract too. As soon as she feels up to it, usually within a week or so, the woman can start doing Kegels when the hormones are trying to tone them up. This has her working with her body instead of against it and she will have a better result. Kegels (also known as elevator exercises) are an exercise she can do while driving, watching tv, doing an office job or while doing dishes. She just focuses on the muscles and tightens them until they become tired and then relaxes them. Repeat. Between the exercises and the protein her muscles should be as tight and firm as they were prior to having a baby. As a rule, a woman's internal muscles will have the same strength and tone as her arms, legs and abs.
The image shows a young woman 6 weeks after giving birth. She has eaten properly and done exercises to strengthen all of her muscles, both internally and externally.