My son is now three years old and he did the same exact behavior when he was 2. My pediatrician told me to let them get their tantrum out, by securing the area around them and not letting them hurt themselves. I had read this also in a nanny book. I took a playpen, shaped like an octagon, and put it in my living room. I filled it around with pillows and everytime he began head butting, kicking and screaming... I put him in there and I stayed close by to observe. He would eventually realize that his tantrum act is not getting him anywhere and calm down. Then I would shower him with hugs. This mainly happens with strong-willed children who cannot verbalize what it is they are feeling... mainly anger and frustration. Once my son began speaking much more that the behavior stopped. It is never to late to pick up a Baby Signs sign language book and try to teach other ways of expressing feelings and frustrations. Call me crazy but it worked for my son. Only now at 3 years old, he has quite the "smart mouth".
Good luck to you!
I run a dayhome, and had a little boy for about a year who at the tender age of 0ne year would if he got the least upset bang his head on the floor or walls. I use to try holding him throuhg it to comfort him but this seemed to make things worse. Then I hit upon a somewhat solution, I would put him in the play pen with extra cushioning so that he couldn't hurt himself. I advised his mother to talk to a pediatrician as I thought he might be slightly autistic, which he turned out to be. So long and short of it, she may not be able to help her behavior, suggest to the mother having her checked by her pediatrician.
Hope things work out
She's very young for any type of treatment I think... Maybe her mom should try therapy and some parenting courses and try to get some idea how to discipline her. Maybe she will be diagnosed with some type of disorder, but she's too young still.
Good luck