Don't go buying her a helmet, that's just daft. It's just what happens with babies and toddlers, they bang their heads frequently when learning to walk/run etc. If they can't be consoled, start vomiting, becoming drowsy, lose consciousness, or there is a lot of blood, then get it checked out.
In two kids, I've only ever got one head injury checked out - that was an ambulance job after a fall of 6ft onto gravel, at a very dangerous angle for her neck, and a lot of blood!
She has balance issues (unrelated to above), has a brain tumour, and several operations on her brain/head in the last year. She hits her head about half a dozen times a day (no exaggeration) sure to get wobblyness. I'm yet to deem any of them serious enough for hospital - they've been minor cuts, bruises and bumps only.
It seems horrifying at first, when they are tiny, but then whacking their head does become pretty normal. Just make sure you know the symptoms to watch out for.