[jennyjuniper]

It sounds as if this woman is running the show and not in a good way. Could you not ask advice from head office? seeing as you are getting no support from the managers directly above you. They are failing in their job too and should be confronted about it.
Have you tried talking to the two directly above you about this woman's attitude and lack of loyalty to the firm? Pregnant or not, she should have helped the customer you mentioned. She could always have taken the rest of her break afterwards.
Looking on the bright side, if she is pregnant she will be going on maternity leave soon. However this lack of support and customer service needs addressing anyway.