Amanda,
It sounds like the vet IV treatment did not turn things around for Maggie this weekend. I'm so sorry.
I know this is a terribly sad sad time right now. But the best you can do now is shower Maggie with love, which you are doing. I'm glad you have her home now. Keep in mind that she doesn't know anything except that she doesn't feel too good and that you are pouring attention all over her. She must be happy about that.
Do keep giving her sub-cu water. being dehydrated is not comfortable from what I have read, so keeping her fluids up as best you can will make her more comfortable for her last few days. After a while she will not want to eat anymore. I guess for me that was the point where I would help them 'cross over'.
Again, I am so very sorry.
Maggie has been so very lucky to have such a love-filled life with you. Just keep thinking how lucky and well loved she has been...her happy life...all because of you and your family.