So, if not a D, who is her late husband in 1941?
MOO JMO
I wouldn't assume a formal marriage and change of name for EB. That was possibly one of her troubles, an informal arrangement that hadn't been regularized.
Children are usually given the mother's last (possibly maiden) name if the father is 'unknown' (in practical terms, is unavailable or unwilling to sign the birth certificate.) They are usually given the last name of the man who signs the birth certificate.
Being a husband and being a biological father are two separate things that are frequently unconnected to each other...
As well, I don't think authorities were as preoccupied with checking ID, as we are now, I wonder what the actual procedure was.
Just to add, the geneology research was probably focussed just on the biological mother, but there's the whole other element of the fathers' as well. Possibly, they were in Alberta.
JMO
ETA: clarifying a bit between what is the legal procedure vs what are the 'social expectations'.
Acccording to police, she was the orphaned daughter of Russian refugees who fled to then harsh and unpopulated Alberta. Fitting in to middle class North American legal system/expectations might not have been easy for a girl in her early twenties. Also JMO
Another comment: 1940 was the middle of WWII. Many men were going off to war and being killed. I'm sure many women had children born, with the father overseas/or killed, and unable to sign the certificate...just another thing that would have been complicating birth records at the time.