What Causes Severe Abdominal Pain With Open Wound After C-section?

my sister had a c-section 6 weeks ago, she had a fall 6 days after the section and since then a section of her wound has opened. she has been having this packed for two weeks but last week developed severe abdominal pain and was rushed to hopsital where they suspect a haematoma but unsually they seem to think it is between layers of the skin and thus may not discharge through her body naturally. She is on iv antibiotics and doctors are still unsure how to treat ?