I changed her food to Eukanuba (better than what she was eating) when
I got her. *Is 3 months enough to reduce shedding by getting her on a
better food? *Does her thick hair mean she'll always shed this much?
Is there anything else I can do to reduce the shedding? *I plan on
making SURE I brush her daily to help reduce it. *I don't think there
is anything medically wrong, as she has been to the vet numerous times
(initial examination, another check-up, and then a spay). *The vet
commented that she had a beautiful healthy coat and nothing seemed
wrong.

I am guessing you are feeding her dry food? I would consider switching
her to an all wet diet. I noticed a significant change in my cats' fur
when I took them off of dry food.

My guess is that you have several things going on: springtime, a
change in living conditions (it sounds like you adopted her, so she
may not have gotten much grooming before), and diet. You might also
consider something like a Furminator. I've owned many pet brushes
before, but this one really, really gets the fur out. Just read the
instructions carefully before use and don't press too hard while using
it.