Maternity and lousy bosses

My wife has been working on contract for a large public organisation for the past several years and started a new contract earlier this year with a different division of the same organisation. Because there was a break of one calendar day between the contracts (a Sunday) and the division is technically a different legal entity (though it uses the same name, branding and shared administration), she was told that she did not qualify for paid maternity leave as she had not completed 40 weeks of service under the new entity. The baby was born 9 weeks premature, so her adjusted age will be only 1 week old by the time my wife's 10 week period of UNPAID maternity leave ends. She recently met her boss to request additional unpaid leave and was received with a very poor attitude. First he opposed the idea and suggested that it would be better if she resigned. Finally he said that the maximum additional unpaid leave he could offer was 4 weeks, which is still extremely stingy. Are there any legal grounds or other tactics to obtain a longer period of unpaid leave? She knows for a fact that another member of staff has been granted unpaid leave for one year for a non-severe medical condition. At the same time, she doesn't want to burn her bridges because there is the possibility of a better permanent position in future with another part of the organisation.

Sent you PM.