FTM, grandma is shaking baby to calm him

me

So my Hubby's grandma (Baby's great grandma) shakes my baby when he is fussy... she doesn't know how to take care of him so to calm him she starts to shake him like up and down and it makes me upset because his little brain is bouncing around in there. I barely rocked my baby and my own grandparents yelled at me for doing it. he is fussy because he needs to be burped after every other ounce ... but instead of trying to feed him after he rejects the bottle she starts to shake him. I told my hubby but he doesn't want to her anything I'm sure. She has had 7 kids? why would she do that?? How do I go about this... the shaking is pretty fast ...kinda like those shake weight commercials lol...