I do at least have her DOB via research done in 2010 by cousin of the person I'm doing the family research for, through http://www.hscic.gov.uk/register-service
which also revealed for 1939 (National Registration?) her husband's DOB and some of their children's DOB that had died. Others living at the same address (in Rhondda) but no details revealed as they were still alive. So I will order the one which I think is her Birth Registration quoting DOB and see what happens. At least if it's incorrect I won't get charged the full amount.