The blood will disappear within a few days to a week after the birth.
The baby should start breastfeeding immediately.  This is not an
uncommon situation, and has nothing to do with breast cancer.  How
likely is it to have breast cancer in both breasts start at the same
time?

Blood in the milk tends to make the baby spit up more, but aside from
that it is of no concern.  She should breastfeed.

Jack Newman, MD, FRCPC