Hi sossle,
You might try checking for your grt-grandma's first husband's WWI death with the cwgc online. just type in those initials and you'll get the website and the search page. If you know the man's name (surname and initial) you're fine. If it's a common surname, you may have to wade through quite a few, and if he gave no one as his next of kin then you might not have a certain record; but it's worth the try.
all the best, Anne.