No, by this point women could own property in their own right, the reason Mary could not inherit, at least initially, was due to the entail which stated that the bulk of the estate is to go with the title, which in turn must follow the male line.
Additionally, Cora's fortune did not automatically go to Robert, she signed it away when she got married. Regardless of what British law might say, as an American, her property would still be covered under US law, at least until such point as she voluntarily transferred it to British jurisdiction such as putting it into a British bank. Gaining a title was the quid pro quo for including her fortune into the entail.
The current entail has the estate going to son George (presumptive), who would then unite both title and all shares of the estate. Note that no other possible future child of Mary's could inherit the title and the full estate, as these inherit from Matthew.
Lastly, bear in mind that DA runs rather fast and loose when it comes to finances, property and tax laws.