This might sound harsh and heartless for some, so just please ignore it if you feel that way.
I think she and you together will need to sit down and make a real hard decision. Definitely be as objective as possible, hold you emotions back and just talk through the scenarios of what IFs and where that leaves the immigration process and your lives together.
I know family is family BUT. It is not a parent/sibling so she could prioritize her new life since the process wasn't short to get where the two are right now.
Even if the worst case happen you can still get married at the court house, no fuss, no party just the formality. Start filing the legal stuff and when she feels ready in like 6 months to a year do the "big" wedding if there is one planned.
You and her have to decide if you want to to risk it and trying the options others suggested (that post is more than 10 years old so who knows, email the consulate). She could say her goodbye on facetime if that comes to that. There is a lot of emotions here so people make rush decisions and not thinking through the consequences.
Unfortunately this is the harsh reality of immigration when somebody gets sick, die, get married etc not always possible to just throw everything away and rush "back home". I am sure a bunch of people on this forum (including me) went through something like this with loved ones where they had to skip a funeral unfortunately. I don't know where she is from so this might be very deep cultural stuff, but her family also should be understanding of the situation.
Best wishes for her grandma and hope she recovers.