If she was exposed to chicken pox but didn't get it, can it still harm the baby ?

Possibly: A person can contract chickenpox, but not exhibit very much of a rash. If pregnant there is a risk of transplacental transmission of the virus to the fetus.

Unlikely, but...: ...Possible. If you have had chickenpox you are immune, and you do not need to worry or do anything. Most pregnant women have already had chickenpox as a child or were vaccinated against it. If you have not had chickenpox, or are not sure, see a doctor. A blood test may be advised to detect antibodies to see if you are immune.

Not likely: If she was exposed and did not get the illness then there is no risk and therefore no harm.