Michelle, as usual, has great advice and thoughts!
This is one the small side, but maybe as it gets closer to time, you and your granddaughter can make some "Big Sister" t-shirts. With all of the stresses going on in your daughter's life, it might bring some smiles to see how excited her two year old is about being a big sister (even if she doesn't "get" it yet).
Then again, if the two year old does get it and is not happy about being a big sister, scratch that idea, lol!
How has your daughter been adjusting to her medications? How is she feeling?