lil - did your partner think of having an xray done at the time of incident? There could just be some tissue damage in that part of the foot. Regarding the swelling, they obviously haven't realised it was so bad, therefore no rest has been taken. I would recon that constantly walking on this foot would keep aggrevating the area, therefore causing the swelling. I would advise them to see their GP for further advice/xray on the affected area, this is your partners best bet. Hope things improve.
Regards