My gm used to ask for Chanel No 5 - so my mum would usually get her the perfume, dsis and I would get the soap/body lotion/talc. Twas great - she loved it, it was a luxury she couldn't have bought herself and it made for easy present buying! She would have been horrified though if anybody had tried to give her just a standard 'granny' soap/cream/talc/pong/etc set as I tend to buy for mil as she never knows what she wants so she gets a tkmaxx or boots special offer special - even at 96 she was very particular about her perfume. To the point that when somebody tried to woo me by giving me a large bottle of Chanel No 5 as a student - I couldn't use it as it just smelt like my dgran - so she got it (and I didn't go out with the guy either!)
A nice small light umbrella - been very wet recently! even if she already has one you can say it's for her to have in the car or as an emergency back up one.
one of those fold up reusable shopping bags
scarf with matching gloves or hat this time
magazine subscription
some places (maybe interflora or even just talking to her local flower shop) will let you give a flower subscription so you get some flowers every month, rather than one big bunch just for christmas, spread it out through the year
if she's getting less mobile, it's worth looking through the catalogue they have at Boots (and probably other places) with things to help elderly people. Dmum's partner struggles to put his socks on and got a gadget to help - was only a fiver or so but really helps him. They have all sorts of bits and bobs to help with different things, depending on how your grandma is struggling. Not very glamorous I know, but would really help out with everyday life. Even things like getting her some of the OXO good grips range of knives and kitchen utensils - the really big handles were originally designed for people who struggle to hold knives etc as the mobility in their hands reduces, so she might find that they make life easy for her. Or a non-slip tray that waiters often use - if she uses trays, helps to reduce the worry about things slipping and falling off when she is carrying them.
Teas-maid to have by her bed
would she use something like a kindle to read on if you kept it stocked up for her? A friend's great grandad got his first one when he was 99 - loved it as it would read out the papers for him as his sight had almost gone.