There could be many causes of a irregularly shaped head. It could be from plagiocephaly due to lying her flat all the time.I got this info on the web:
"A number of studies have associated the recent dramatic increase in the number of children with flatten heads with the "back sleep campaign." Since more children sleep on their backs, more have some flattening of the back of their heads. This condition can be much worse on one side if a child preferentially sleeps with that side down. Positional (or deformational) plagiocephaly, also known as flattened head syndrome, results from preferentially lying on one side of the head."
Another cause could be from craniosynostosis where the sutures (openings of the skull) fuse too early. There are different types of cranio: Saggital which is the elongated head (like a football), metopic (triangular shaped), lamboid (where more than one suture is closed) and coronal (where there is bossing on one side of the forehead). My daughter had the last one. One side of her forehead had a bump, while the other side hardly had a forehead and was flat. Her eyebrows were misaligned and her eyes were not the same size. She had surgery at 5 months and is now 5 and looks perfect. She also had a slight head tilt (torticollis) when she was a baby and she had therapy for it. There could also be other causes which I am not educated about. Your best option though is to see a pediatritic neurologist so he could find out what is causing her head to have this shape. Good luck!