You've got to communicate with her. Ask her how she feels. If you explain that there's little risk to either of you, and if anything happens you'll take full responsibility, she'll probably understand. Tell her that nobody will know, there won't be any dealers needed because you'll grow it yourself, and it would be highly unlikely that law enforcement would ever be involved, considering the circumstances you've described. You also must explain that to be strong and healthy for the eventual surgery, this is definitely a method worth trying.

I hope that she can see your point of view. I think she will.