never tried posting anything here before so here goes...
 
our 4.5 year-old female, chestnut, had this exact problem a few months ago.
the vet diagnosed it as an abcessed anal gland possibly resulting from
incomplete descenting.  she was on antibiotics for 10 days, and as you
noticed with missy, the abcess cleared up completely.  the vet had
recommended, though, that we bring her in after the antibiotics to basically
redo the descenting, otherwise the problem would reoccur, as you
experienced, so that's what we did.  no further problems.  since missy's
case sounds so similar to what chestnut went through, i'd guess she'll keep
having trouble until she's descented again properly.
 
since this is my first post, i'll introduce myself and my weasels.  i'm
wendy.  that over there is my husband jim.  over there scratching at the
back of the couch is molly, a 2.5 year old female who also loves digging at
the carpet.  over here with her head in the refrigerator is pete, another
2.5 year old female (her name was originally 'la petite' but that's too hard
for us anglophones to say so we changed it) who is constantly begging for
treats.  and of course, there's chestnut, who has a pot belly (enlarged
spleen, the vet says) and no hair on her tail, but is cute in her own way.
all three of our girls came from the ottawa ferret association last january.
 
i've been lurking around here for a couple of weeks now and taking notes on
all the neat ideas people talk about.  just thought it was an appropriate
time to share the benefits of our experience.
 
wendy
[Posted in FML issue 1411]