Terry,
I usually counsel a mom to use milk pumped during a yeast infection within a
day or two, and discard what they can't.  I have big blocks of yeast in my
freezer which work beautifully when defrosted on those rare occasions I have
time to bake bread!  High temperatures do kill yeast (I beleive above 140
degrees F), so theoretically warming it above this would do the trick, but it
would also denature the beneficial proteins, including sIgA.  I know we all
hate to waste a drop of precious milk, but if the mom is still lactating, she
would probably be better off not taking the chance of another bout of
suffering.
Catherine Watson Genna, IBCLC