Our hearts go out to your Mom, Amanda . . . she has really been a "beamer" to us as well.
Having just lost my Yorkie 6 months ago, I know losing her chihuahua will be a real blow to your Mom. I agree with those who feel it might be better to wait until she gets home to tell her. One of the hardest things I had to adjust to was not having Summer run to the door to greet me whenever I came home. If your Mom knows about her doggy before she gets home, the entire trip home will really be hard for her . . . and arriving will be even harder. And if she asks why you didn't tell her at the hospital, tell her that you didn't want her to dread coming home.
I am so sorry for everything she's going through. Please give her a hug from her friends at FoRT . . . and thank you for keeping us in the loop on her progress.