I tried this because of all the raves it used to get and I thought it was horrible. It dried my hair out ALOT. I was going through a stage where all I wanted was long thick hair and I would try every long,strong,thick treatment/conditioner out there and none worked for that. Some made your hair feel thicker or feel healthier (which helps it look thicker/better) but none actually made my hair grow faster or made me grow more hair from my scalp. I agree w. the vitamins though they def. made my nails grow thicker and faster, it was harder to tell if the vitamins made my hair grow faster because you can't watch it as closely as your nails. But since nails and hair are basically the same thing I assume the vitamins helped my hair. But back to the Mane n Tail I really disliked what it did to my hair all the way around.
And for your sister, I have a sister w. beautiful long long dark shiny thick straight Dk Dk brown hair she could use dishsoap and let it hang dry and it would come out shiny and bouncy and beautiful... and.... I have curly curly blond hair that has a very coarse texture , it costs me a fortune and takes countless amount of time,products and treatments and lots of blowdrying,flatirons,and other tools just for it to be decent hair ...her coloring and hair is like my parents and although I look like my dad I'm not the same hair or anything. It's just like that sometimes ..even if its unfair lol