Definately get it checked out. There is a condition called tortacullus (sp?) which is a shortening of the neck muscles causing bubs to turn her head to one side. Chiro alone probably wont help if this is the case. Physio will sort it out and they'll teach you how to do the stretches and help.
We went though it with DD, her head looked very similar to your beautiful DD. I used both physio and chiro and her flat spot disappeared very quickly. But things you can do in the mean time is put her toys to one side so she has to turn her head. When you hold her, hold her on the side that she has to turn to look forward. Anything to encourage her to look to the other side.

You've picked it up early so she will be fine