Hi Trish,
I haven't had to search for any deaths of a woman who married twice so I really don't know. But I have found that the 'other surnames' field is particularly useful as a cross-reference tool
My understanding (which may be totally flawed!) is that the only name(s) used for indexing death certificates are the name(s) of the actual deceased - hence men only being indexed by their surname and not using the name of anyone else on the cert e.g. wife. And since women may have more than one name, it helps when looking for them rather than looking for men. I am sure that there are situations where men are known by more than one name and it will then be useful for searching for those particular cases.
Cheers,
Clare