1. Pregnancy in family is no reason to avoid transfer.
2. Transfer can be challenged only if it is found that the same is done as a measure of punishment.
3.However check whether the PSU has any Rule in favour of a lady who has a pregnancy in the family. I am sorry there may not be such Rule.
4.If she is indeed harassed then she make a written representation to higher authority on this issue of castism and then challenge the transfer in high court.
5. The harassment is valid reason to challenge the trasnfer. However beofre going to court do ask her to explore all possible means to settle this verbally with her higher authority.