Well, I gave some citations above....and of course, the information can certainly be obtained as political contributions over $200.00 must be reported.  Guessing you'll find your grandmother's name on the official filings.....

The site that LifeoftheLay referred to has been awarded a Pulitzer Prize, and has been referred to by many news organizations.  Actually - and oddly enough - it has been referred to as a "progressive" site.  They are funded by a relatively diverse bunch of folks....
https://www.publicintegrity.org/about/our-work/supporters