My mom has thin hair and needs a medium to low maintenance cut that's sassy and young.
I wanted to cut her hair into a graduated bob... how do I do it?

Thin hair?? Maybe not so good to cut into a bob. One of the charms of a bob is swinging a lot of hair around when you turn your head.

Consider it could be a disaster depending how thin her hair is.

Sweetie, if your mom has thin hair and wants a hair cut that will make her hair fuller, I recommend that she get some layers put into her hair. The layer cut will add volume to her hair. To prevent a botched hair cut, it's best that your mom consults a hairstylist.