I lost my mom to breast cancer, too, 12 years ago now, and the shadows of her and my dad, lost nine months after her, are all over Disney. Since my parents took me and my sisters to Disney nearly every year since it opened, family memories are intricately woven throughout many, many places that are still virtually the same as they were in the 70's. Though I rarely visit Port Orleans Riverside (which will always be Dixie Landings to me) these days, I smile whenever I walk down the long hallway from the entrance to the food court because I remember my kids when they were little running full tilt down that hall to leap into my mom and dad's arms on a family rendezvous (we lived in separate states and often met up there). My mom's favorite ride was the Haunted Mansion and my dad's was Pirates of the Caribbean, so I never miss them. I see what is possibly still the same bench I sat on with my mom with my head in her lap by the Crystal Palace when I was 13 and so sick waiting to go lie down in the "Mickey Mouse hospital" and then, hours later, feeling miraculously healed after a cool, dark ten minutes in the Enchanted Tiki Room. I can stand on Main Street even now watching a night parade and feel the presence of my mom beside me dancing to the Main Street Electrical Parade music or Spectromagic (though those parades are long moved on) because she was always so happy to be at Disney with her family and couldn't help bounce to the music. It was because of my share of the inheritance from my parents that I was able to buy a DVC membership and I truly feel like that is my parents' way of treating me to Disney trips for the rest of my life they way they did the first part of my life.
I am very sorry for your loss. Disney visits, particularly over a lot of years and growing from a child to an adult and then as a parent yourself tend to become a part of your soul, and the "first Disney visit without..." a special person in your life is always going to be gutting. The comfort to me, as I hope it will eventually be to you, is that you will be able to at some point soon get on a ride or eat in a restaurant or sit by a resort pool and remember your mom being there and it will be a source of happiness.