I tend to agree with the above question re: X-rays at least. One would want a close examination of any boney lesion before commenting. How are you diagnosing a haematoma? i.e. bleeding causing the swelling. She may have just traumatized some superficial vessels that are easily damaged each time they are knocked, hence recurrent bruising.

Any image you can post for us? Is there any issue with dorsiflexion contractions? Infection would usually be clinically considered if there is warmth in that area compared to the other leg. Of course fresh bleeding could do the same. Let's get a plain x-ray as a starting point.