Poison ivy can spread from person to person if the person who came in
contact with the oil from the plant spreads the oil to anything else --
which they often do.  This includes the bed sheets, bath towels, faucet
handles, clothes, etc., as well as direct person-to-person skin contact.
The oil is very persistent and long-lasting on clothes.  One hint for relief
from the pain and itching is to run extremely hot water over the affected
body part -- as hot as you can stand, or slightly hotter.  This obviously
may not work well for breasts, but just as a general hint.  It's great on
feet, legs, arms, etc.  It feels good while you are doing it, and then the
itching seems to go away for several hours.  There are also now
over-the-counter cremes that create a skin barrier between you and poison
ivy oil.  The mom might want to get that and put it on her child (everywhere
externally) to reduce the risk that oil from the mother's hands or clothes
or other body parts might be transferred to the daughter.

Kathy D., wife of someone who gets terrible poison ivy rashes