how to rejoin split hairs?

The only way to solve split ends is too get your hair cut. Nothing will actually mend the split ends. Once your hair is split (damaged), there isn't anything you can do about it. Instead of completely getting my hair cut, I go through every once in awhile and cut out some of the split ends. This makes my hair look better and is always an option so you're not cutting all of the hair. You can prevent splits though, and that means not using a blow dryer, avoiding hairstyles that can damage hair, using a leave in conditioner, and conditioning while in the shower.

Anything that uses heat to style the hair dries it out and causes split ends. Once she has had the ends trimmed off (that's the only way to get rid of them) your girlfriend should get a quality moisturizing shampoo and conditioner. Letting her hair dry naturally instead of using a hair dryer will help the hair retain the moisture.

There is no way to rejoin split ends. Once hair has split, that's it. All you can do is trim the split ends off and try to care for your hair from that point on. Like someone else said, styling the hair takes a big toll on it. Also, shampooing and conditioning the hair damages it, even though a lot of people do not realize this. Hair is somewhat fragile and think of it this way, hair grows about one half inch a month so it takes about 2 years or so to grow it to your shoulders. Over two years hair takes a lot of damage. That's why regular trims are important. Anyway, if your girlfriend styles her hair a lot (especially straightening, blowdrying, or dying) then that is probably causing the split ends.