I'm a hairstylist. It is very common for hair to change color and texure as we age. Hair usually darkens, and fine childhood hair usually becomes more course and unruly as well.
Issues such as thyroid can dry out hair, but it often causes thining as well.
Also, some medications can cause hair changes. If she is on a special vitamin, supplement, medication, check with your doctor to see if this is a symptom. If you have hard, well water or drink lots of mineral water, it can cause hair courseness as well.
As for helpig her love her hair, eating a healthy, well rounded diet, drinking ,lots of water and protecting it from the sun are the basics. Use a good shampoo and moisturing conditioner daily. About once a week, you can use an additional conditioning mask. Towel dry softly and comb out from ends to roots. Blow dry it with an ion dryer and a flat brush, lightly curling under at the ends. Blast it with the cool shot at the end to smooth the hair cuticle down for a nice, shiney surface and to set the style.
Follow up with a small amount of gloss syrum.