Swollen ankle...

Any ideas?  Agnes has a swollen ankle.  Fully weight bearing, not limping, foot has been examined and no redness or damaged areas, no broken skin, seems to mainly confined to the ankle, pad is a bit swollen too and warm to touch  Leg ring is still loose so nothing constricting it.  She doesnt mind being picked up and us poking around with it.  She is eating and drinking and seems her normal self.  She doesnt perch so dont think she has fallen.  Bumblefoot perhaps?  Any other clues to what it may be?  Have washed it, used antiseptic and confined to quarters.