It had its moments.
It would be funnier if she talked in a more elderly, fragile voice. It would make a more suitable contrast to all the head exploding and what-not.
I reckon it might be good to have her perform common, stereotypical 'grandma' activities and then have the demon emerge to cause havoc, rather than just randomly have peoples heads explode. The last scene in particular is a bit of a cop-out to the viewers after they endure that car ride which seems to be building up to something.
Also, the voice clipped at one time...digital clipping is not cool, its just lazy not to remove the distortion or do a retake.
Anyway, it was funny to some degree I guess, and the animation was a good effort.