Each province in Canada has strict rules for the the number of years that must pass before birth/marriage/death records can be made public. Some provinces then have free access to view these documents online, other provinces charge a fee for them.
Each province adopted the division of death registrations and medical registrations at different times, I believe. Being that it is 1911 in question, there might be the very slim chance that the registration would contain cause of death, but as their site states outright that it will NOT state that, makes me think they would redact that part.
As to newspaper articles, there is no mention of Nellie in Saskatchewan (so far), and the numerous articles on John Henry Wesson that are of a biography style cover his early life, then jump to 1912 when he married. There is no mention that the 1912 marriage is his second.
Looking in the British papers, there is an article on the wire being sent of Nellie's death. In it they state that she made the trip well, and was in good spirits and the cause of death they could not state (I take that mean they weren't told?). I would think your suspicions could well be right.
The British papers also have an article on their wedding.
I will take a longer look tomorrow in case I missed something, (it's late here!). If you cannot access the British papers and would like the articles, do let me know. (I can't post the British articles here for copyright reasons). As John Henry Wesson is technically not related to you, you may not want any articles on him, but should you wish to see them, I will gladly clip them and send you a link.
JH Wesson became very well known and did well for himself; how very sad that Nellie couldn't be a part of that.