Ok... Sorry I have to be the adult here.
This is a very bad idea. Eventually it will be found, You will be in BIG trouble and you will have to find your ball python another home.
I know how you feel, I loved snakes as a kid, and which according to my mother "snakes are not something "normal girls' like". In fact my mom now blames herself for my Snake (& reptile) obsession because she deprived e as a child. But now I have my own house and she can't do anything about it. Nanana-NAH Mom!
Ophidiophobia ( fear of snakes) is not something that can easily gotten over. Most people who are afraid of snakes are REALLY afraid of snakes.You really need to respect your grandmothers fear.
Do you have a friend who is into ball Pythons too, who's parents don't mind the cold blooded pets? Maybe you could keep yours at his/ her house. Snake friends are the best!
-----
"There is a fine line between a hobby and mental illness"
