My thoughts:

1) Stress and fatigue-- this in and of itself can be the culprit, or it could
be the immune-weakening factor in the presence of an organism.  Mom may need
help with stress and fatigue management; if she has depression problems, is a
counselor involved? If so, perhaps some brainstorming with this person, and
with your input (protecting and promoting bfg) may be helpful.

2) Need to culture the milk!  If the usual cure-all doesn't work, we *have*
to take this step and stop casting into the dark so that the *appropriate*
antibiotic can be selected.

3) Possible obstruction-  bras and sleeping positions are the obvious first
questions, but perhaps this mom has a cystic-type lump that is obstructing a
duct?  I don't if this can be detected well during lactation with
ultrasonography, but it's worth a thought.

Quite likely it is a combination of some of the above. With a few more facts
pinned down and some rest and help, mom will have a much better chance of
recuperating.

-Lisa Marasco, BA, LLLL, IBCLC