I wish I had a photo this nice to remember my wee granny by
If you want a technical appraisal, I would go along with the change in perspective as mentioned before, I would even go quite wide, 50mm equivalent, 35mm eqivalent, your gran had a kindly face and whilst this image will bring you happy thoughts it wouldn't really tell anybody else about your gran.
I like environmental portraiture, does your gran have a favourite or personal room with her own photos on the wall? sideboards etc? Grans usually have really interesting rooms full of memories and textures and fabrics and patterns, cool ornaments etc. It would be great to get a nice image like that, the image of a family woman, surrounded by a lifetime of memories of her own.
Rather than a formal posed image why not just get images of her at a family get together, my gran had a comical way about her, telling stories, sharing the gossip, her eyes could tell you 1'000 opinions.
I just feel that there is no personality in your image, if your Gran is anything like mine was she'll have an opinion on just about everything and be happy to share it, get some of that personality out.
I personally think that studio portraiture and formal poses are very sterile and cold, and for such a personal and intimate subject you should try and get away from that.
Maybe a more even light (softbox would be ideal, overcast window or outside light perfect, little tiniest bit of fill flash to get the catchlight.
And remember to tell your gran you love her, I'd swap all my camera gear and an arm and a leg to have the chance to do that once more.