Spaying her probably helped.
Cats have a social heirarchy, based primarily on gender.
Intact males are (generally) at the top.
Then are neutered males
Then come intact females.
Then neutered females at the bottom.
There's some variation based on size, age, personality, and who has claws (declawing lowers them, as does age and smaller size; larger cats are higher).
Your older cat may have felt threatened just because of the age/neutered factor. Now, there is only the age factor.
As long as the younger cat is respecting the older one when they growl/hiss, it should end up okay. :)
"Life is good; flight is better." --me
"Growing old is mandatory. Growing up is optional!" --my dad
"Never give up. Never surrender." --Tim Allen as Jason Nesmith in "Galaxy Quest"
| Pounds lost: 21.0