What Could Cause Knot Like Lumps At The Incision Site After A C-section?
A few possibilities could be there.
Given the nature of the swelling which you've described, it could be an incisional hernia but the timespan is just 6days so it's unlikely.
Since it's painful also, there may be a possibility of hematoma formation (a swelling of a clotted blood inside the tissues), or even tissue fluid collection (which seems likely) or even puss collection (which is another possibility given this timeframe and painful nature of the swelling). In case of the last scenario (abscess/puss collection), it means the area is probably infected and she may require further antibiotics therapy until full resolution of the infection.
Please discuss with her doctor (it'll be better if you get hold of her operating surgeon as s/he would be the best person to analyze it in depth) regarding these additional issues and proceed further.
Let me know I can assist you further. Take Care.