Help! Appleyard duck with very swollen/infected toe

[grakat]

Hi! I need some help. My appleyard duck got a small cut on her foot a few weeks ago. I cleaned it, used hydrogen peroxide a few days in a row and kept an eye on it. It had seemed to fully heal well, but a few days later i looked and it had swollen again. There is no scab or opening to the outside now, but it is very swollen and she is limping and holding it up when she stands still. i was thinking i should open it to get infection out, but if have no idea where to cut. the black spot in the pic by the way is not a scab, it seems to be a discoloration. Not sure. Thanks!

 

[Mallards and Quail]

I've never had that happen. I'll tag someone who may be able to help.
@New duck mommy 2021